Can doesn't mean "necessarily will". It depends on how much attention the comment attracts a lot of times, even more than on its content. Things that anyone could say in anger on a bad day or as dark joke can come back to haunt you if they happen to raise a media circus. Yet, advocating genocide can have no effect in your career if it goes broadly unnoticed. That's part of the problem.
Can it though? Because I see some vile comments made by people who appear to be using their real name, photo, location information on their profile.