Breeding rodents for feeders isn't rocket science. The issue is that you went to where there's a more pet owners/breeders than reptile and feeder-breeders. When you go on a site full of pet breeders/show breeders/pet owners, you can't start spouting off about how you're throwing live pets to a snake and not expect to get some blowback.
What if someone came here who owns snakes and also started talking about how they were going to raise a lot of cheap balls up to make leather from them? Would most of the people here think it was okay as long as the snakes were killed humanely? Would it matter that in the wild, snakes are killed all the time in horrible ways by other animals or by humans to harvest meat and skins? No, because THIS is a forum devoted to people who love snakes as pets.
Most rat breeders who breed for pets or show are correct in thinking that breeding rats isn't easy... in THEIR goals. To get a good conformation, great color, great coat, great disposition rat that will live a long and healthy life takes a LOT of work to combine the right lines to get exactly what you want. To breed a healthy feeder takes much much less work. They don't understand that a feeder rodent doesn't need to meet conformation rules or coat color particulars. It also doesn't matter much if they COULD grow to only 2 years old or they would make it to 4 years old... when most are killed at less than 6 months! What matters is litter size, health and growth.