If I do my homework and do all I can to provide a good home for a difficult fish and it dies; I'm not going to feel any more guilty than I would if I order the grilled halibut at dinner tonight. Funny; a few days ago, there was a thread applauding the entry of PetSmart into the saltwater business. I don't have any facts; but I'll bet Petco (and now PetSmart) will be responsible for more lost fish, because of the inexperience of the staff and mass marketing approach, than "difficult" fish lost by all the worlds serious fish keepers. I know this is a big issue with many folks; and I'll always respect their opinion.
ps. How do they identify larval fish? These usually live in the huge masses of "larval soup" along with countless other forms of life. What happens to all that life that is netted along with the larval tangs. It just doesn't seem possible to me that someone could pick out one larvae species from that huge mass. "Baby" fish; maybe.