The government has many tools to discourage behavior that it has determined to be undesirable. Among the least intrusive is a public education campaign, i.e. propaganda. The most intrusive is prohibition with the application of severe penalties.
Somewhere in the middle is increased taxation. This raises the opportunity cost of such behavior and reduces its practice while not prohibiting it entirely. In nations that value individual rights and personal freedoms this is the preferred approach.
If undesirable social consequences are to be avoided it would be wise to take a considered approach with a set program of escalating government intrusion that matches social expectations if the government is to be successful in the behavior modification. It is not a quick fix and can take a few generations before previously ubiquitous and acceptable behavior becomes socially unacceptable.
As far as smoking goes the government discouragement campaign is a fairly new thing since until lately smoking was not considered a problem by anyone. The public education campaign, a first step, is only one generation old but has had an effect both in decreased undesirable behavior and increased social expectations. These increased social expectations have pushed government to the next level, increased taxation specifically targeted to reduce undesirable behavior and mitigate its social costs.
We should pray that social expectations do not go so far as prohibition because the consequences of that will create new more grave problems that will be quite costly and socially destructive. It is questionable whether prohibition brings more social benefits than costs. The "war on drugs" should be a caution to those keen on prohibiting individual behavior that impacts others only indirectly.
As far as being overweight goes, that is in its infancy as a socially undesirable behavior and is more a biological problem for many people than a strictly behavioral problem. Not everyone is naturally skinny. Besides that, the perception that all fat people are an automatic health risk has not been proven. Inferences have been made and statistical studies point to an increased probability but that is about it.
Increasing taxes on certain foods to combat obesity is not targeted like increased taxes on cigarettes. Increasing health care premiums on overweight people who pose no health risk is discriminatory. Prohibition is out of the question.
So, what tools can the government deploy to combat obesity without encouraging discrimination against those who pose no risk and are thus innocent?
P.S.
There are also many smokers who require no increased health care than anyone else throughout their lives but that is a strictly voluntary behavior so any excuse to discriminate against smokers is far less fraught than the issue of obesity.