From what people were saying about hand rearing. You don't have to hand rear if you don't want to. If the parents mess up the first few times then you can just let the chicks die and the parents will have hopefully learnt for the future.
Skipping over the fact that I could never just let a chick die if there was any way to save it, many breeder birds don't "learn" over time to be good parents. Some do and some don't. Let's face it -- even the best breeder with the best aviary set-up and the best nutrition program simply can't replicate, completely, the conditions under which parrots reproduce in the wild. Also, captive bred birds often don't know what to do in a breeding situation and can't just "figure it out." They needed parents and/or a flock to teach them, and they never had that.
There are a huge number of breeder birds out there who aren't good parents and never will be. I sort of alluded to this in my previous post, when I said you would need to be really cautious in buying pairs of birds. Breeder pairs are for sale for a reason -- and the reason is often that they aren't good parents. Someone breeds the pair, discovers that they kill their babies, doesn't want to hand feed from day one, and advertises them as a "proven pair." Someone else buys them, discovers that they kill their babies, doesn't want to hand feed from day one, and again advertises them as a "proven pair." The parents are repeatedly "rehomed." Babies repeatedly die.
I disagree, in general, with the idea that no one should be breeding parrots. If no one breeds parrots, every species will eventually disappear as pets. However, I absolutely agree that MOST people shouldn't be breeding parrots. And no one should be breeding parrots if they aren't prepared to hand feed babies from day one.