Eh, it's a sad fact of life that rats are just take a low-to-intermediate step on the food chain, but snakes have to eat too.
My roommate breeds for snake food, not as her primary source, but as a supplement to buying frozen. She's very good about making sure the doe is in superb health, and never breeds them too often (2-3 times per doe, with lots of space in between). She euthanizes them at around 3 weeks (at the really cute stage! I couldn't do it!) and freezes them.
Honestly, I think it's probably better for the welfare of all animals involved that she's breeding every once in a while for food. You don't know what kind of conditions the rats who are feeder-bred were born into, and breeding healthy animals means high quality food for the snake. The does are treated extremely well, also, so the rats involved live quality lives and are treated as humanely as possible.
So, while I'd have a very hard time doing it myself (especially considering her corn snake can only eat baby rats at the adorable stage where they're zooming and nibbling on everything) I don't think that it's inherently a bad thing as long as it is done so that the rats being bred & those being fed are treated well.
Finally, I've seen the warehouse of the local feeder-breeder in the town where I went to college. The conditions were awful, and all of the rats had such bad myco problems that the warehouse sounded like it had a cricket infestation. The rats were really inbred, and they were producing rats with myco problems from birth. That's not the kind of stock you want to breed, even if they're going for snake food. They're weak, inferior rats, and they should never be allowed to further those genetic lines. That's not the kind of business that should be supported. Perhaps there are professional feeder-breeders out there that have great conditions, but I doubt it.