Consul wrote: There are many far-fetched logical possibilities which needn't be taken seriously, because they are mere possibilities. Of course, there are scientific problems concerning empirical (behavioral and neurophysiological) criteria for other minds/consciousnesses that need to be taken seriously;
Red flag. Fundamental problem there. Why did you ever think other people were conscious. Is it because you were attempting to extend the range of reductive physicalism? No, it was not. The whole enterprise of understanding or explaining consciousness can be thought of as "anti-science" on its face. Just admit it, you're going with your gut on this one.
and there are questions which are very difficult to answer such as What's the earliest/oldest species of conscious animals? and How many species of conscious animals are there?. But these problems don't justify general skepticism about other minds/consciousnesses
All skepticism of causes of behavior which are not reductive physicalism is justified in reductive physicalism. What justifies going outside of reductive physicalism - at least as a long-term goal. Isn't this where all science wants to go if it can?
or the existence of a (mind-independent) physical reality.
Science cannot really even begin to address this issue. Personally I'm going with my gut in saying that there is a reality "out there".
As Wittgenstein remarks: "Braucht man zum Zweifel nicht Gründe?"/"Doesn't one need reasons for doubt?" Do I have rational reasons to doubt that I am not the only conscious being, that there are many (human and nonhuman) conscious beings, or that there is a (mind-independent) physical reality? – No, I haven't!
This is the human bias - and it clearly is a bias. Bias shows when you have a proposition and its opposite, and you declare one to be the *clear default* and the other requiring extreme justification aka "no reason to be skeptical" of it.
-- Updated October 21st, 2017, 11:19 am to add the following --
see Hans Christian Andersen's "The Emperor's New Clothes"