Would I like a BETA? Hell yes!
Would there be one? Heck no.
1)Players wouldn't be able to do anything about overpowered guns. First off, you would only get a couple of guns in a beta and you can't get a real sense of thigns without the whole layout. Second, I think most people that complain about weapons have a terrible sense of what it really means to be balanced.
2)As far as maps go, did you mean glitches like under the map or something? Again, you're getting maybe two maps in a beta, and the chances of people finding something wrong is extremely rare. There's a small 1337 community that spends their lives doing things like that. Nowadays though, because of the massive about of people that Treyarch bans, people don't even waste their time with glitches like these that can get them banned. ON TOP OF THAT, Treyarch has the ability to hot fix issues very quickly. They're really on top of things like these.
Activision (they have to make the call) wouldn't even think twice about a beta. They know that from past sales, the hype will remain high, so they wouldn't want to give away any piece of the cake until customers pay for the whole thing.