If I had a dollar everytime...
If there was a rule against teaming, you could run into serious trouble.
My father is a lawyer, and I like to think I am similar to him in these circumstances. If I were caught teaming in a team over 3/2 I would simply say "I wasn't teaming with them, we were just near each other and not killing each other!" It would be exactly the same as people picking apart laws. Think about it.
To make this rule fool-proof MCG would have to make the rule pages long, and you cant just STOP people having fun. I agree, the amount of teams are large, but I just think to myself "You play in teams, Guy, they're only having fun."
In conclusion, MCGamer will never have a rule against having fun by playing together. It would also make about 1/2 of people who play leave and start playing the server that shall remain nameless. As a great player once said "People forget that games where invented to have fun, not invented so that you could pick up your computer and throw it on the ground."
~Otto
PS: I hope I explained the first part well xD