I see where you are coming from.The part that boggles my mind .
think about it .
someone buys a kitten or puppy .
if it does , are they going back and buying another and another ?
no but corals and fish are different ?
With any animal there are life spans and even health issues coming into the hobby. I do feel corals and fish are less pet like than a dog or a cat AND can live much longer than a dog or cat. I have green striped mushrooms and brown button polyps that I have had since 2000, but unlike cats that I can spay so they don't produce offspring, my mushrooms left unchecked will overtake my tank.
With marine fish there is a lot of loss just in collecting and transporting. I've heard that many fish in the hobby are still caught with cyanide ( many food fish are caught this way for the Asian market). There really aren't a large amount of cultivated fish for sale in the hobby, so you have to find the good collectors that treat their fish properly.