Ideas are bulletproof.
By this I mean that you can not just remove the whole concept of clans with the click of a button. Removing clans as a forum section will not make them all disband at once. It will simply force clans to use a new medium for applications, rosters, results and possibly communication. Obviously, there could be a rule saying that "Clan wars are not allowed on MCGamer", but people could easily just say that they are a group of friends playing against each other, which would be a very hard point to prove wrong, without having to use evidence from any other websites or third party services like Skype and TeamSpeak. Yes, you could just reduce the team limits, or make a rule against teaming, but I'm not even gonna start that whole debate on this thread.
Anyway, in the end, what would come out of making an anti-clan rule, and removing the clan section on the forums? A lot of angry people. Nothing else. It would not make clans disappear, which means that the disadvantages of having clans in the community would still be there, and the only group affected would be clan members, who would get mad about the whole case, possibly start flaming a bit, but most likely just move on, and use a new medium.