The moral status of abortion is irrelevant to the question of whether “don’t harm babies for fun” is a moral universal, because no woman gets an abortion because “abortion is fun”
"You are only making abortion legal because you want to have sex (read: fun) without consequences" is not an uncommon argument against it.
If you want to argue that this isn't what "for sport" means, you just circle back to the point I made earlier. It is even harder to define what is for fun and what is not than to define what is a baby.
I think there’s a clear distinction between (1) doing an act because you find it fun in itself, (2) doing an act because it eliminates an unwanted consequence of some other fun act.
When I say no woman gets an abortion “for fun”, I mean there is no woman for whom abortion belongs to (1); when some pro-lifer claims women get abortions “for fun”, they are talking about (2) not (1).
My claim that essentially everyone agrees it is immoral to harm babies for fun is talking about “for fun” in sense (1) not sense (2)
The moral status of abortion is irrelevant to the question of whether “don’t harm babies for fun” is a moral universal, because no woman gets an abortion because “abortion is fun”