I'd feel much better about clicking the Karma buttons if they were biased on individual post, like in reddit or on support sites and not the actual poster.
I feel that by rating the poster rather than the individual post, it forces one to be more accountable for what they write. It's not a perfect yardstick by any means, but it works well enough most of the time.
Take, for example, VJose32. He's operated here under a number of aliases in the past, usually by simply changing his profile's name. But no matter what name he chose, his negative reputation followed him. I do confess that I had a hard time with him as well, because he was exceptionally negative in much of what he wrote everywhere: this forum, UC, company Facebook pages, etc. It was as if he never had a kind word for anyone. I've ranked him down a few times in the past and apparently many others did as well. As a result, his rep dropped well into the negative numbers - I think it was around -40 at one point, plus or minus a few points. It's not the lowest I've ever seen here, but it was in the bottom five for certain. (The forum used to allow immediate "thumbs up/down" to the same profile, whereas now it forces you to wait an hour before you can affect the same profile. A kid made a comment early in the forum's history about how he'd taken a few dings to his rep, only to see a few people gang up as a practical joke and knock his numbers into the negative triple digits. It's been reset since then, but people from then on were discouraged from complaining about taking negative hits to their rep.)
Back to the topic at hand: he reached a point where he was trying to create a new identity by making a new profile. I had a PM exchange with him, agreeing to bury the hatchet and restore his reputation to zero as long as he agreed to work on showing a little more positivity or at least tamping down on the negative comments. I pointed out that he's got a possible brand name going for himself - he's a popular video reviewer on YouTube - and that he should work to protect his image rather than tarnish it.
It worked for a brief while. I gave him a boost for one good post, and someone else must have done the same as he went up to about 3. But he couldn't maintain it for long and his rep dropped again, back into the negative numbers. It's still in the single negative digits, and I'm hoping for a turn around but I'm not holding my breath, either.
The point is that his reputation number was important to him and it really did prove to be a barometer of what people thought of what he was writing. He's not the first people to mention this to me. Others have commented that they wrote something a bit on the negative side, thinking it would be well-received but they noticed their rep number falling a few points, put two and two together and decided that maybe that wasn't such a good idea after all. As far as that goes, it appears to be working as it was intended.
If it was just posts we were ranking rather than people, someone could write something utterly horrific, get voted well below zero, but vanish for a few days, reappear with a new name on the old profile and unless someone spotted the name change, no one would be the wiser. As this isn't the case, people are forced to own up to what they say and in general they behave more civilly in an effort to preserve their reputation.