Unless you aggressively moderate to keep quality high, question and answer sites inevitably degenerate into Yahoo Answers, as the bad poisons the pool and drive

Unless you aggressively moderate to keep quality high, question and answer sites inevitably degenerate into Yahoo Answers, as the bad poisons the pool and drives out the high quality users. If you aggressively moderate to keep quality high, you drive off low quality users, and stall out your growth.