Great topic IMO and a lot of very valid and insightful points are being made here. Here is my take on reef keeping and fishing in general. There is no question that commercial food fishing operations are one of the greatest threats to the oceanic environment (the other being degradation of the environment in general), and that commercial aquarium livestock fishing and sport fishing have a miniscule effect compared to the other factors. I know a lot of anglers who catch and release (it seems to me a large percentage of sport anglers are in this catagory now) and the fish they catch and release are in infinately better hands than a novice aquarist with a 20 gallon tank. In the big scheme of things, neither sportfishing or the aquarium trade is going to have a significant impact on the environment by itself. We are however a convenient target for environmental groups.
The part of this hobby that kills me is seeing LFS's continuing to sell completely innapropriate fish and coral species to absolute beginners, knowing full well the organism has no chance at survival (the LFS owner knows there is a much better chance of making another fish or coral sale when this one dies), the amount of garbage like this that continues to go on in this industry just digusts me. The goal in shops like these seems to simply to sell livestock as fast as possible and make as money before the person quits the hobby in frustration. The majority of shops I have personally visited fall into this catagory unfortunately.
With rare fish, those of extremely limited geography, or hard to keep species I think they should be left in the sea whether common or not. I think that some species have shown themselves to be so notoriously difficult or innapropriate for home aquaria that further importation only harms our hobby in the long run. My one exception to this thought is when I see experienced or dedicated aquarists trying to keep a difficult species in order to unlock some husbandry secrets, this type of experimentation has helped our hobby greatly IMO. There is a difference between a noob keeping a moorish idol in a 30 gallon because he liked "Gill" in finding nemo and a veteran fishkeeper trying to figure this species out.