As evidence of this, think of how many people think that $other_party wants to "destroy America" in some form. Cue (and possibly queue) commenters saying "but $x really does want that!"

I've found that people who claim to know the other side's motivations are projecting for the most part. I catch myself doing it too. Being more aware of bias does not make one less susceptible to it, unfortunately. If anything, it tends to bring overconfidence regarding it :/