Because in his completely fucking crazy brain -- [Sorry Ace, he tries not to insult your family, Garp included, but he was just punched in the nuts in what can only be described as rousing memories of Garp's punches.] -- that would save your life and set you on the best path towards happiness. I don't agree with him, obviously, or we wouldn't be nakama, but even I can see why he'd think that.

And let's just say you and Luffy get up to a lot bigger trouble, and since he definitely can't be around, I think he appreciates that you do your own thing in spite of him. In you know... a weird kind of backwards D way. Don't punch me in the nuts again for all that or I'll break my rule and kick you.

And yeah... he'd laugh a lot. I'm getting a headache just picturing it.