Tate wasn't a killer.
He never wanted to hurt anybody even in his thieving days.
Ok he might want to hit some people but he wasn't a killer.
Not even Jack who set him up. Jack who let him spend seven years in prison alone and had no problem with letting him walk the dead man's walk.
Tate was no killer.
He didn't want to do it even on the boat when Jack's betrayal was revealed and Jack was actively trying to shoot him.
Tate was no killer.
He was good once.
Tate was good with his mom and with Nina. He was still angry and had his walls up but he wanted to be good again.