I once had about 2# of pressure on a 4# trigger, with a 1911 aimed at a bad guys center of mass from about 15 feet away. The guy made the wise decision to release a woman and he then slipped back into his house through the front door. The woman got away, the police took it from there. That was the one and only time I had half of a trigger to go until BANG, and feelings per se had nothing to do with it, just instinct and training.
If I had shot the guy, I'd have felt bad about taking a life, but better about saving an innocent life. The good of the saving would have outweighed the bad of the killing, for a net good. That's why I would say many feel "good" about killing. It's a net good, in saving innocent human life from a predator.