I'm not aware of his experiments so I can't speak to the results, but I am aware of the overarching theories surrounding the effects of biases people have in society between one another (it's a popular research topic given the last four years). I understand that most people aren't inherently "evil" in the sense that they wish ill harm onto the other party, and that often times people with the opposite ideas simply have a difference in beliefs.There is an experiment that has been repeated many times. In it you take people who oppose each other politically they have to explain their opponents position until the person who disagrees with them agrees they have correctly articulated it. So a democrat and republicans each have to explain each other’s positions to each other’s satisfaction. Haidt has done this and consistently people on the right can do this trivially and people on the left struggle. Your post is an example of one possible reason why - many of the left lack empathy for their opponents because they ascribe malice to all their ideas and so cannot bring themselves to articulate them to the satisfaction of those they disagree with. Try it sometimes. It’s a good exercise because it helps us understand one another.
That said, I certainly could have incorrectly believed someone else is truly malicious - especially over an internet forum with strangers, where there's very little benefit of the doubt I can truly provide others. Which is why you'd often to have to go with wondering whether they're speaking in good faith or not.