I believe the sustainability of wild caught ornamental fish stocks should be down to the governments of the countries where they are caught. The ornamental fish trade is an essential part of economic stability of many communities. I believe it does have its positive aspects for the local environments where the fish are wild caught
I also believe that the aquatic trade has been responsible for the preservation of species that would otherwise be lost last time I checked the humble red tail black shark was EXTINCT in the wild, its a common kept fish but only became so because of the demand brought about from the original wild caught stocks, the wild caught stock popularised the fish which led to its captive breeding not the otherway round.
I dont believe there is a harm in keeping a wild caught fish as long as it is a sustainable level. I DO NOT believe that wild caught fish will be unhappy in the environment I provide for them, If I felt wild caught fish would not be happy I wouldnt keep captive bred fish in the same situation either. I have happily caught and kept wild fish myself.
I also believe a bigger question than wild caught or captive bred is whether the immense suffering and death caused by the aquatic trade at all is morally justifiable. Anyone argueing for captive bred only probably hasnt seen the conditions the farmed fish go through to get to their LFS, or the fatality rates of the neon tetra that take its price from 9p at source to £1.20 or so in the LFS! Our aquatic hobby whether wild caught or captive bred only supports needless wholesale deaths of fish, not only in the hands of "bad aquarists" but also as the normal course of things in the supply chain before you even pick your fish out of the display tank.
Your "captive bred" tetras are shipped 2000 to a bag with no filtration, no major oxygenation and cooling down to 18oC for a 24 hour cross the globe trip, fatalities before the point of sale can be 25%+ (whole shipments of 2000 tetras are known to turn up dead!) I accept that this is the reality of the situation - I like to keep fish its the only way I can get many of the fish I like to keep. I accept that many fish may die to make it possible for me to keep the ones I want to keep, its sad but that is the reality. Is a captive bred fish dieing any better than a wild caught fish dieing?
I enjoy breeding fish I support the idea of selling more locally bred fish, but I dont believe that theres a pressing need to bring in huge amounts of bureaucracy and licensing to the hobby. I dont believe ornamental fishing is causing huge damage to wild populations of many species of fish, certainly nothing like the damage caused by food fishing.