Why do people have to teamkill for choppers in bad company 2?

Two matches in a row people teamkilled for choppers, its getting annoying, im on your team so dont kill me, besides first come first serve in my opinion, he was the pilot so i jumped in to be the gunner but no, he is such a moron that he has to kill me so he can have the chopper to himself only to find out he cant pilot one and he crashes 5 seconds later, then i guess these guys were butt buddies and had to teamkill me so they can have their precious chopper, if people already have the chopper im not going to teamkill for it, but if i get in a chopper dont teamkill me, if someone does teamkill me for one im going to kill them back and take what was mine in the first place, and no im not going to be an idiot and kill the guy who is the gunner.