Hello; A few counterpoints.
My guess is that most home fish keeper tanks are not the last repository of species that would otherwise be endangered in the wild in their natural habitat, at least for now.
There are numerious posts describing severly overstocked tanks. Many have stocking so dense that a few hours without electrical power has been reported to result in loss of fish.
Perhaps this is not generally true, but the large majority of active fish tanks I have personally seen over the last five decades have been very poorly kept. It would be hard to say for sure, but my feeling that the some of the worst have been in fish shops. I have seen many home tanks in horrible condition. I no longer try to encourage folks to take up the hobby as far too often hey have wound up with very bad results.
I have read of collection methods that are very destructive. The most recent that I recall reading about involved the collection of ottocinclius. If you want to buy a leopard skin coat then some agent will act on your desire and go out and convince a leopard to donate it's skin. We spend money on fish and our paid agents collect the various fish. My best guess is that there are a very large percentage of losses by the time the fish get to a local fish shop.
For the few fish keepers, I know of, that do a good job with their tanks the fish spend their lives in the tanks. There are laws that stop tank fish from being placed back into the wild. All of the fish that I have kept over the years, with the exception of the ones that I have now, have died. They existed for my pleasure.
Those in my tanks now are very lightly stocked and likely have very decent living conditions. I would very much like to but I am not able to discount all the fish that passed away during the several decades it took me to learn how to keep fish properly and in very low stocking densities. I did not have the internet for most of my fishkeeping time and perhaps could have learned much more quickly had such information been available. I would had to fight the tendency to want to fill up a tank with fish for a long time.
So, as much as I like keeping fish I have to concede that there is a level of what could be called "cruelty" involved. I like to think that most of the problems for fish end when I get them home, but I realise that the fish trade exists in some part because I am willing to spend the money that I do.