People are free to create duplicate forums and compete IMHO. I think the problem right now boils down to the way you discover new forums. Right now it's just one big alphabetical list - but that will change soon enough and the best performing forums will be shown. 

I don't want to prevent duplicates simply because we may end up with a situation where someone doesn't like how someone else is moderating, so they want to try to do it better.

As for inactive forums - I do agree, though I'm not sure what the terms of that might be. Very likely a problem to solve next year though when we actually have things we'd consider "inactive" :)

Good things to think about though!