I can talk about a similar (karma-like) system on another site. It was a wiki-style site popular from 2006-2010.
Their original system counted a user's creations and edits. There was the expected amount of drama around who had more creations vs edits. Creators tended to add a lot of high volume but low effort crap. Editors would get a lot of grief over 'stealing' entries because the idiots who created the site put the username of the last editor at the bottom of the entry.
It got worse.
Around 2008 the idiots reimagined the site and expanded the scope. They kept the shitty idea of keeping the last editor's username, but they added a points system tied to how many new features were added. For example: if you added a town you were awarded 1 point, but if you added a street or river you were awarded 1 point for each kilometer of road or river. Shit got real weird.
It was a race towards crap. AngrySteve59 was no longer at the top of the list. He was replaced by GamerJoe84 who had racked up shit points using the new system.
Points just seem to make people crazy. "Rate me! Evaluate my work" - Lisa Simpson