You're talking about filtering types of speech but in reality you really want to block people. It's not that Bob is really enthusiastic about Purple; it's that

You're talking about filtering types of speech but in reality you really want to block people. It's not that Bob is really enthusiastic about Purple; it's that he's an insufferable jerk that makes any conversation about Pink impossible. You think you can try and compete with Bob but you can't; he's mentally ill and spends 6 hours a day posting about it. You could try to make a rational argument about the evils of Purple but it dosn't matter. You confront Bob but he's not interested in rational conversation. You just get more frustrated and eventually give up on your community. If there is still anyone still interested in Pink they've long been driven off.