I have to say, I’ve always admired the Stack exchange system. Yes, it’s a Karma-like system, and it’s obviously not perfect, but it means that accounts always start with very little abilities, most notably that they’re not able to downvote yet. And when those accounts do get the ability to downvote (which doesn’t come all too quickly), it costs a certain amount of their “reputation”, which makes them think twice about downvoting.