There is actually no real evidence that power feeding will shorten their lifespan. It's assumed that it will due to experiments on other animals, but there is no actual proof that power feeding will shorten a ball pythons life.
I think that it's difficult to overfeed babies, they're constantly growing and putting all of the food they eat into growth, however if you continue feeding the same way once they reach adulthood, they will become obese, and obese snakes do not breed well.
Personally I like to keep my hatchlings on the hungry side because I think it's easier to get them switched to frozen thawed that way, but I certainly wouldn't call the breeder a scumbag because he likes to feed a lot.