Honestly, killing your teammate just because they took a vehicle you wanted is the most asinine thing I've ever heard.
Yet it happens all time. Kind of stupid of 343 if you ask me though. Remove friendly, but leave it on for vehicles so that you can run over teammates and they can blow you up/EMP you. Well that was 1 step forward, 2 step back.
I think they weren't planning on the sheer stupidity of some people. That some people would sink to killing their teammate just to ride in a special vehicle.
"What is a man? A miserable little pile of secrets!" ~Dracula