Ooh, blue collar shaming. How quaint.
Are you familiar with reductio ad absurdum arguments? One type, associated with Socrates, is when you take an apparently innocuous position to its logical extreme. If the extreme appears absurd (or contradictory), then logically the original position is invalid.
Your premise is that it's morally acceptable for "marine aquarists" to collect tropical fish for their own use as long as it's done with due care to the fish. I don't agree. "Marine aquarists" literally means anyone with a saltwater fishtank, there are no licensing or certification requirements for this hobby in the US. Thus, according to your premise, anyone who wanted to collect tropical fish could do so for the cost of a basic saltwater setup. You mentioned no limits on size or rarity, other than what you could reasonable care for. So whale sharks and Mantas could be on your collections list if you were rich enough.
But taking this back down to Earth, I happen to like seeing spotted drums and basslets in their native habitat. I do think it would be unsustainable if anyone who wanted to collect them from the wild was free to do so.
Note that I have nothing against private aquariums (I have a basic freshwater setup myself). But I do think they should be stocked from the offspring of already captured fish. Even taking the Gulf Stream stragglers means at best you are taking meals away from another bunch of marine organisms.
One last thing, because I know it's going to come up. Of course there are much worse abuses of the marine environment than fish collecting. But we are not talking about that here.