As a left wing anarchist, I think it can be ethical justified to use direct action tactics ranging from a beautifully painted mural on a building you didn't have planning permission for, up to sabotaging badger traps & pushing past a fox hunter in order to save a fox from getting mauled to death by dogs.
Our hope on the far-left, is that our ideals and passion can be admired by some, like risking prison to sabotage the draft for Vietnam, so some peoples sons aren’t conscripted into fighting an evil war.  Then any moderate left policies might look conservative in comparison which if adopted will make them the tried and tested policies of the future.
To quickly summarise, the direction the far-left would like to head in, is going from; a two party system, to… a multi-party coalition through preferential voting, to… some local government positions being elected by sortition, to… the majority of society being so content with worker-co-ops and syndicalist unions that we transition from representative democracy to direct democracy. So, a chamber of ministers to federated spokes councils.
Fascists will also use tactics from civil disobedience to political violence, and tend toward violence against people for people holding ideas as the things they hate, rather than the lefts systemic critique of material conditions. All in the hopes of pushing society towards a more authoritarian constitutional republic, before seizing power in a palace coup and attempting to rule as a sequence of dictators for life.
And then there are a range of reasons between these two political positions that people might desire to use civil disobedience & direct action.
It is up to everyone to decide which government to vote in, to enact what degree of punishment to bring down on people breaking the law on either side. And any direction the society goes in for either not controlling or bowing to which protesters demands is still the moral culpability of the government and those who participated in the party political process.
For me, there simply is an obvious legal and moral difference between for example victimless civil disobedience on the left aimed at all people being treated equally in society like collecting salt from the sea or staying seated on the bus, to the type of violence you see on the right, like Israeli settlers throwing people off their land with arson attacks, stealing another country’s resources against international law.
But again, it is true that to whatever degree those on the left chose bad targets optically, we do to some degree bring the slow pace of change on ourselves or hand the right an advocacy win.
Here are my thoughts on a range of tactics and I'd be interested to read other people's own thoughts:
Civil Disobedience – Whether it be breaking the law without causing any damage or economic sabotage and political violence which we’ll talk about later, anarchists hope to chose the right actions to provoke conversations and materially challenge unethical industries and actors, so as to push electoral politics towards direct democracy and eventually consolidate our gains in a revolution.
Graffiti & Culture Jamming – Whether it be an artistic masterpiece that no one asked for or altering a billboard to say something funny and political, instead of the advert that was there before pressuring you to consume more and more, most people can be won over by this as a good form of advocacy. Just don’t practice tagging your name a million times over every building in town.
Hacking – I think most people agree whistle-blowing war crimes is a yay. Selectively releasing documents to help conservatives win elections however, is a nay from me.
Sabotage – I think the far-left should chose targets which have caused people the most amount of misery, for which people can sympathise most, like the sabotaging of draft cards I wrote about at the beginning. So causing economic damage to affect material conditions and make a statement.
The far-left also needs to carefully consider the difference between property which is personal, luxury, private, government owned and co-operatively worker owned.
So, it could be seen as ethical to chose material targets of evil actors in order to cause economic damage and make a statement, so long as in the case of personal property, the item has no sentimental value and can be replaced because the person is wealthy. Or is a luxury item that was paid for through the exploitation of others labor. Or is private property, meaning the means of production which should be owned collectively anyway.
It’s an expression of wanting to find an outlet for legitimate anger against that which causes us suffering. For example, if taking the risk to slash slaughterhouse trucks’ tires in the dead of night is how you develop stronger bonds with a group of people and gain the confidence to do amazing things like travel the world and learn from other liberation struggles.
Fighting – First off, I think propaganda by the deed, physically hurting people for the purpose of making a political statement is evil, as it runs counter to our philosophy on the left that material conditions create the person and so we should make every peaceful effort to rehabilitate people.
However, to the extent that some current institutions fail to rehabilitate people and the process of seeking justice through these institutions can cause more trauma, then I personally think that some forms of personal violence to get to resolve feelings of helplessness in the face of evil acts can be an ethical act.
For example survivor-led vigilantism: 
Other examples we can think of are personally desiring to fight fascists in the street to block them from marching through immigrant communities. To pushing your way through huntsman to save a fox from getting mauled to death by dogs.“I wanted revenge. I wanted to make him feel as out of control, scared and vulnerable as he had made me feel. There is no safety really after a sexual assault, but there can be consequences.” -Angustia Celeste, “Safety is an Illusion: Reflections on Accountability”
Two situations in which prominent anarchist men were confronted and attacked by groups of women in New York and Santa Cruz made waves in anarchist circles in 2010. The debates that unfolded across our scenes in response to the actions revealed a widespread sense of frustration with existing methods of addressing sexual assault in anarchist scenes. Physical confrontation isn’t a new strategy; it was one of the ways survivors responded to their abusers before community accountability discourse became widespread in anarchist circles. As accountability strategies developed, many rejected physical confrontation because it hadn’t worked to stop rape or keep people safe. The trend of survivor-led vigilantism accompanied by communiqués critiquing accountability process models reflects the powerlessness and desperation felt by survivors, who are searching for alternatives in the face of the futility of the other available options.
However, survivor-led vigilantism can be a valid response to sexual assault regardless of the existence of alternatives. One doesn’t need to feel powerless or sense the futility of other options to take decisive physical action against one’s abuser. This approach offers several advantages. For one, in stark contrast to many accountability processes, it sets realistic goals and succeeds at them. It can feel more empowering and fulfilling than a long, frequently triggering, overly abstract process. Women can use confrontations to build collective power towards other concerted anti-patriarchal action. Physical confrontation sends an unambiguous message that sexual assault is unacceptable. If sexual violence imprints patriarchy on the bodies of women, taking revenge embodies female resistance.
I’ll work through hypotheticals from circumstances relevant to the past, present and future, then talk through the ethics of each.
Most people agree anyone who took it upon themselves to assassinate Hitler a day before the break out of WW2 would be seen as committing an ethical act, no matter who follows, because throwing a wrench into the cult of personality spell built around Hitler would be a significant set back for the fascist state’s grip over the people. And given all the evidence pointing to the inevitability of war, such an act could easily be seen as a necessary pre-emptive act.
Most can sympathise with quick revolutions against dictatorships where the result is a freer society, like the Kurdish uprising in Northern Syria which took power from a regime who had rolled tanks on demonstrators and outlawed teaching of their native language.
But, even there, there are key foundations you need to work from, like the probability you won’t just give an excuse for the oppressor committing even worse horrors as was the case with the Rohingya militants who ambushed a police checkpoint, resulting in army & citizen campaign to burn down many villages, plus murder and rape those that couldn’t get away.
As well as a responsibility to put down arms after winning political freedoms and a majority are in favour of diplomacy through electoral politics, like in Northern Ireland today.
Under representative parliamentary systems, the sentiment of most is that even if it could be argued that a war of terror against the ruling class was the easiest route to produce a better society, that it would still be ethically wrong to be the person who takes another’s life just because it’s the easiest way. Since regardless of manufactured consent or anything else you still could have worked to build a coalition to overcome those obstacles and change the system slowly from within.
And I agree, it would be an act of self-harm to treat life with such disregard when you could have been that same deluded person shrouded in the justificatory trappings of society treating your behaviour normally. I don’t think the way we win today is treating a cold bureaucratic system with equally cold disregard in whose life we had the resources to be able to intimidate this week. Time on earth is the greatest gift people have, to make mistakes and learn from them.
So then, an easy statement to make on life under representative parliamentary systems is; outside of absurdly unrealistic hypotheticals, I could never condone purposefully killing others when campaigning against such monoliths as state and corporate repression today.
Breaking that down though; what do I mean by an unrealistic hypothetical? For example the philosophical thought experiment called the trolley problem, where you have a runaway trolley hurtling towards 5 people tied to a track, and you can pull a leaver so the train changes tracks and only kills 1 person tied to a track. Or you can change it to 7 billion to 1 even. Or 7 billion of your average citizens vs. 1 million unethical politicians, police and bosses, to make it political.
Now what do I mean by purposeful, well we can think of for example the most extreme cases of post-partum psychosis which has mothers killing their babies. But more nuanced than that, the rape victim who gets worn down by their abuser for years until they have a psychological break and kill.
That does still leave a lot of lee way for people knowingly taking risks with others lives, not intending to kill, but who are reckless in their actions, such as with some forms of economic sabotage. And I agree such a reckless act would bring up feelings of revulsion for all kinds of reasons like questioning whether the person was really doing it to help people or for their own ego-aggrandizement. All that can be hoped is a person makes a careful accounting of their ability for human error and weighs it against the outcomes of doing nothing.
We can hypothesise the unrealistic case of 99% of society desiring a referendum on a shift from parliamentary representative system to a federated spokes council system and the MPs dragging their feet, the same way both parties gerrymander the boundaries to make it easier to win despite it being the one issue most everyone agrees is bad, and people needing to storm the halls of power to force a vote to happen.
More likely though, an opportunity for a far-left revolution might arise from such a confluence of events as climate refugees and worker gains forcing the state and corporations into trying to crack down on freedoms in order to preserve their power and enough people resisting that move, who are then able take power and usher in radical policy change, with either the army deciding to stand down or splitting into factions.
1. The Camden 28 – The Camden 28 were a group of Catholic left anti-Vietnam War activists who in 1971 planned and executed a raid on a Camden, New Jersey draft board. The raid resulted in a high-profile criminal trial of the activists that was seen by many as a referendum on the Vietnam War and as an example of jury nullification.
2. Accounting for Ourselves – Breaking the Impasse Around Assault and Abuse in Anarchist Scenes.