Why not? I would like one where people are not allowed to go in circles, at least make them work new arguments for subsequent posts. I would not abuse it (i.e. not tag all of them), but we saw how ridiculously off track the thread about Guerrer's work went. Depending on the topic, it could be desirable. Also, since it will likely be argued... No, I don't see it as a form of "censorship", new threads are cheap and nobody is preventing offshoots.
"Deep into that darkness peering, long I stood there, wondering, fearing, doubting, dreaming dreams no mortal ever dared to dream before..."