In theory, it's an organic and flexible way to indicate bad actors and that that are healthy for a community. If you get the ranking system done right, it makes trolls and assholes easy to weed out of your usage, and let's you know there's community trust in someone.
Which has all kinds of flaws even without manipulation of the system because people are fucking dumb, and you can't always trust the majority. If you're a virologist on an antivax forum, your karma will be shit. But you'd still be a valuable person to have around, despite being a troll within that community.
And no, you can't totally negate any human systems from having that kind of perception flaws. Humans are dumb. At best, you could manually counter it, but that has flaws of its own.