Quick disclaimer- I've only been hit with negative rep once, and it was quite a while ago. I can also count on both hands the number of times I'm aware of giving negative rep- and those were all to posts that were borderline being reportable- just outlandishly rude and inappropriate. I have NEVER given someone negative rep because I disagreed with them or disliked what they said.

That done, I see this pop up on the boards fairly often- people saying that they've been given negative rep on a post, and in looking over their post there wasn't anything worth giving negative rep for, other than someone apparently disagreeing with what they said. Here's what it says when you try to give negative rep:
Disapprove (e.g. Inflammatory, Derogatory, Disruptive, Trolling, or violates community guidelines)
Seems pretty clear to me- that's not just because you disagree or don't like what they say. You give negative rep because someone is essentially doing nothing but stirring up trouble, and not even being polite about it.

You shouldn't give it just because you disagree with someone. You don't give it because you don't want to accept what they say, even if they are right. You don't give it just because you don't like someone. You give it when they are crossing the lines of proper behavior.

At least that's how it's supposed to work. I find myself giving positive rep to people who have been hit with neg rep when they shouldn't, and it really bugs me when I see abuse like this. If anything, neg rep given for the wrong reasons is, itself, abuse of the system, the mods can (and do) review it if submitted to them, and you can get in trouble for improperly giving negative rep.

I'd love to see what others think and have to say about it.