Frankly, I see no witchunting or demonization anywhere in the argument I, at least, was having with the cosplayer, but I claim the right of commenting on the photo according to the feelings I got from it.

Putting a photo here is launching it in a public space and therefore exposing it to the potential criticism from the people that are, for the good or the bad, affected by the content of the photo, so commenting on it is a perfectly appropriate action.
I actually don't get why you are so defensive, even more than the cosplayers themselves.