The result is that we create a picture of a monster (e.g. in this case, a dishonest person fucking up the country) that has an uncanny ability to push our buttons and drive us crazy. I puzzled over my own version of this for a long time before realizing that the only being with such perfect knowledge of how to push my buttons was me.
So we're fighting demons of our own creation. That explains why we can never get away from them or ever win: they're internal creatures who have access to all our secret codes—probably better access than we do.
Knowing about this dynamic is key to not being driven crazy by it. In my case it was an occupational health hazard. I had to figure it out because the alternative was literally to have my buttons pushed and be driven crazy all day, every day. There's more than enough material on HN to fuel that, and it isn't a good way to live.
Once you realize that this process is going on inside your system and isn't a snapshot of reality, you can be more open to information that doesn't fit the picture. For example, that the person you're talking to admires your desire for honesty and has as little power to fuck up the country (or unfuck it up) as you do.
Your last sentence is a contribution of its own, and I agree with you—it's primal threat circuitry that's being activated. That's why arguments on the internet are so tiring!
I don't have much incentive to group my comments together, but I do use HN as a place to post mini-essays from time to time—to get stuff that's been on my mind off my chest. The problem is that you'd have to wade through reams of "personal attacks are are not allowed on Hacker News" and "we've detached this subthread and marked it off topic" to find them.