It begins when some members post in a thread that a mod deems inappropriate. How does the mod try to teach them to control themselves? He bans everyone who posted.
Personally, I find it ironic and ineffective. If the original post is truly appalling, ban the OP and ban those who made it escalate and turned it into a war. There are innocents in every one of those threads, and banning them doesn't even seem worthwhile. I've seen people purposefully escalate threads into flame wars, post completely irrelevant comments which derail threads, and commit much worse than those people who posted innocently in those spam threads.
I get that the mods are not able to moderate every thread all the time, but from a contextual standpoint, I just don't see the point in carpet bans.