Trolls will be trolls no matter what you do.

If you turn FF off they will block your shots or find some way to abuse you.

Have you played MMOs before? Griefing happens considerably less.

Not really, most are paid

trolling and griefing can happen also without FF, in some case FF help removing trolling or griefer or exploiter, and similar.
bodyblocking field of vision blocking.
imagine someone that stop in front of teammate iumpin, or blocking base access/road with undestructable vehicles.
don't need to be troll can even be enemy faction that roll on another faction for sabotaging.

it's all about mentality: if someone want to troll: will find a method, if someone want to exploit will find a method, is someone want to grief other player will find a method.
PVE game with no form of PVP is full of people that abuse vs other player.

a classic example:

I would rather not. Makes the game run a lot better when you're not worried about accidentally running into your buddy's line of fire. Or his melee swing.

Nooo, it makes the game a lot easier. Not necessarily better. Generally we want to punish people for rushing into things balls-deep. This includes crossing in front of your buddies that are laying down a line of fire.
We're going for an immersion feel, and if I could cross freely through my side's blizzard of lead and not take any damage that'd feel pretty stupid.

Friendly fire, is a must, it be a little odd, to have a comrades bolter to back of head, do NOTHING.

Look, I would like Friendly fire I think it would be good, But for the inexperienced players it would not not good (For Example if a little kid or n00b has a tank and hes shooting his team mates). I would find that highly annoying. So that is why I voted 'No' ahaha

Well, that guy is very swiftly going to be lacking a tank when his teammates turn around and unload plasma cannons on his rear armor. Not to mention that I BELIEVE that tanks are going to be rather expensive as far as requisition goes so that's a very large investment just to be an ass and he'll suffer the more for it.

Once you TK 3+ people you should get a mark put out on you and nobody should suffer consequences for killing those people. I wouldn't suggest an xp reward though, as that might encourage a few people to just grind out xp through griefing.

We'll police our own ranks. A mistake is understandable. Two 'mistakes' are lethal.