If people are breeding parrot fish, it's the same as breeding puggles. You don't like it, we don't like it, but someone likes it and is buying them. Or they wouldn't be making them.Personally, I'd never condone breeding mixes period. I've always found it strange that intentionally cross breeding is somewhat acceptable in the dog world. I'm a fishkeeper and it's a given that certain fish should not be kept in the same tanks as other kinds of fish for the simple reason that they will cross breed. Parrot fish are looked down on in most circles simply because they are hybrids. There are many fish keepers who will deliberately cull hybrid fry. It's interesting to me that in the dog world cockapoos, puggles, labradoodles and the like are intentionally bred for profit.
It depends on the situation. If I'm at work, I usually just change the conversation. If it's a personal conversation, I take the same approach as Dogstar and ask what they do with the dogs (show, agility, field trials, etc) and about the health testing.
I had a good friend who still thought females needed to have one litter. Once I talked to him about the realities of breeding he had a very open mind and realized it wasn't a good idea at this time.