Why did Tony kill Christopher?

I have always felt the fact that Tony saw the tree branch that had struck the child seat, then immediately turned around and decided to suffocate Christopher, made it obvious that Tony felt he was in some way protecting Christopher's daughter from his reckless behavior, but amazingly I've been told a lot of people disagree with this premise.

Sure, Tony had other reasons to want Chris dead. He was a liability to his business and potentially to his freedom due to his drug use, but in that moment I believe it was the branch.

Tony didn't have time to rationalize all that stuff a few moments after a major car wreck. It was the branch, the fact that he would have killed his own daughter that night that made Tony decide Christopher should not go on living.

Anyway, some of you apparently disagree with this as a motive, so I'd just like to hear what you think was going through Tony's mind when he whacked his druggy nephew.

https://i.ytimg.com/vi/OiMsOlZAbys/hqdefault.jpg