When I first joined I went back and read many of the old threads searching for a fellow Aussie. As a result, I read many of the posts of the most frequent contributors. It was also apparent that many of the topics were the most controversial. That's an Aussie trait for sure, shit stirrer!
It's hard to be certain because if I give someone a -karma it updates their profile so shows the progressive total, whether you are looking at their first post or their last. It does seem however, based on comments, that -karma was earned by those that tended to piss people off because they were the most controversial, right or wrong I'm not judging. People got them because they earned / deserved (?) them.
Even in the short time I've been around, people seem to have decided there is merit in having the most -karma so now some contributors seem to be asking for them whether or not they have earned / deserved (?) them or they are being given to people as a means to boost their credibility, for whatever reason.
I think the old way was the best way, you got them because you earned / deserved them!
If you piss them off you'll get a +. If you make them laugh or give them something to fap to you'll get a -. Kind of backwards but hey, no one is perfect.