I somehow dont think you will get a balanced discussion on the ethics of fishkeeping on a forum dedicated to fishkeeping.
There are obviously downsides to keeping any animal in capitivity, but what you can do is minimise these by providing the best environment you can reasonably set up. Are the conditions some people keep fish in cruel? Absolutely. Is this generally the case? I dont think so.
The fish have easy access to food, with no predator issues. If they get sick they get treated. Those small annual fish can easily live 2 or 3 times their normal annual lifespan relatively stressfree. Do they have the space the have in the wild? Obviously not. Is it an issue?
I think the ethics of destroying natural habitats to capture wild fish for the hobby far outweigh whether a fish will grow to its wild, natural size in an aquarium.