'Nasty' comments can be difficult for humans to spot, let alone machines. A lot of important information is lost when we go to a strictly text only medium. If we're going with the group to decide what's good and what isn't, then we run the risk of group think as well. So I am a little cautious about endorsing any automatic filtering of content in this way.
People who are new also, have the ability to upvote but not downvote. I think this might be causing a disproportate amount of upvoting, which may also pertain to 'nasty' comments. Perhaps maybe disabling upvoting for new people for a certain period and/or after a receiving a certain karma score might alievate this a little?