Is George justified in killing lennie? why does he feel he has to do it? list at least 3 reasons.

George isn't justified, but he wants to do it himself and quickly before Curly or anyone else does it hatefully with a rope around Lennie's neck.

George has no choice. If the mob didn't torture and kill Lennie, they would (at the very least) lock him in a cage. As Slim said, "that ain't no way to live". George could not let the situation go any further, he could no longer protect Lennie.