I agree with Mick.

I think that Tony---due to his childlike temper---was capable of killing anyone in his criminal life on the spur of the moment. I think that Ralphie was at the point where, due to his son's condtion at the time, wasn't going to lay down to one of Tony's tantrums. And if he didn't have Justin weighing on his mind, he probably wouldn't have even argued the point with Tony. But he was full of remorse over his son and just didn't give a shit anymore. And it cost him his life.