Exactly. No one in the military is allowed to pull the trigger willy-nilly without authorization. That's what the assholes at Haditha got in trouble.
And no, that shouldn't be the attitude of the helicopter crew, but when you're about to pull the trigger on someone and take away somebody's father, brother, son, cousin, etc..it's stressful. I really, really, really doubt these guys take pleasure in killing anyone. If anything it's just a mental defensive reaction on their part.
Frankly, with the intel they had at the time and given the situation, they did the best they could. When a recon platform picks up radio calls indicating a bunch of insurgents operating in an area, and then a camera spots a bunch of armed folks walking around carrying what looks to be an RPG near a helicopter...