Wouldn't it take human readers to separate out the trolls from the new posters, and wouldn't such human readers need to be paid for that work? I'm assuming a lot, granted, but isn't this site volunteer work? Who would want to slough through the new posts to remove the trolls from the new people?

Ok, that could sound sarcastic. It isn't. I really don't think that many people would volunteer for such work for long, and I honestly don't know about any computer programs that could make that sort of judgment about posters.