It's your opinion that it's 100% unacceptable. You seem to think everyone's life is mighty precious for someone claiming that they would have shot a man dead in his back yard.
Belief is not fact. They needed to find out if they were connected with any terrorist groups and at the very least find out why they did it.
They did try to catch Bin Laden alive. The mission that killed him was aimed at bringing him in, not killing him. He chose to fight back and Seal Team 6 chose to kill him. His death was significant. The death of a 19 year old "scrub" isn't.