We cannot discount the fact that people give negative karma because they contradict of what the other members are saying, or because they just don't like the guy, it really happens on an open forum, So far, I seldom get negative karma, maybe because I don't like to be in a drama but most of all, I follow the guidelines and avoid topics that I cannot contribute positively.
I agree with everything you said, and to be honest, all those things are true. I believe some people do send negative Karma to someone whom they don't like and or for other obvious reasons. But, I believe those people should understand that they're somehow misusing the karma system of the forum.
I'm also among those members who doesn't get more negative karma as compared to positive ones, and that's because I don't really offend others with my words and I believe useful conversation is way better than arguing.
I often send positive karma to the ones who I mention in my posts because I truly like their posts and as appreciation I send them positive karma. Sometimes I do mention +1 when I send karma to someone while other times I don't mention that but send the positive karma for sure.