I agree that intentional team killing deserves a ban. Sure, it's clear when there are no reds and some blue is obviously gunning for you, the problem is that many times people accuse others of doing it intentionally when it is just an accident. I can't imagine any way for the game coding to determine intent.
Sometimes it can be nice to take a break from the constant rage of war.
Team killing can be good for collective tanking sessions, circus flying or just general goofing off. If friendly fire had no effect it would be a little tougher to have some kinds of fun.
It would also make it so there was no consequence to sloppy shooting. One of the tactics I use is to move so the reds are lined up as they shoot at me. I do it in hopes that either they will accidentally team kill each other or that one of them will simply hold their fire. Decreasing the number of bullets coming at you can be good, no? It also makes it so you can shoot at more than one of them in a single burst of fire.
But what about
"strategic team killing"? Is there such a thing? Imagine that you have just bombed a carrier and are heading back to reload. Would it be wrong to ask a teammate to shoot you down while you're in tanking range? Wouldn't that help your team's chances of a win? I'm guessing that some of you would cry bloody murder! I can imagine the flaming posts! Would it change anyone's attitude if it were in a "squad wars" situation?
I think Zup has a good solution on this one: Three strikes and you're out. Period.