Comment by Arnt

That raising an animal for slaughter is permitted.

You can't separate those two; the choice doesn't happen between the raising and the slaughter. Farmers don't breed animals and only then consider whether to slaughter them, the choice happens earlier.

So the argument is that letting an animal see the light of day on condition that it'll be slaughtered at the right age is a valid thing to do. (Digressing: my own opinion is that it depends on how the animal gets to spend its time on earth. But that's just my opinion, not really relevant to the argument.)