My 2psi:
Underwater hunting (spearfishing, lobstering, scalloping etc.) is GOOD if done sustainably and humanely. In fact, it's far better than "normal" commercial fishing methods which are quite destructive. And there's something that just seems more fair about doing it by hand. Kill your catch quickly regardless of whether you think it can "suffer" or not, follow the regulations, do not overharvest, don't take anything you don't plan to eat, don't take juveniles or big breeding females, do not take rare or threatened species, don't damage the habitat while you do it.
Pertaining to man-made artifacts and wreck stuff - I'm not going to get into a long ethical tirade, especially because my position on the matter is far from settled. But a few notes:
- Artifacts being recovered, then just left to collect dust in some random cabinet where nobody except one diver knows they exist is no good. So many things end up being thrown in dumpsters by family members when those divers pass away.
- Proper cataloging, preservation, and public display are important if artifacts are recovered.
- At the very least, tag every artifact you find with a label that says where and when it was found and what it is. This also makes collections cooler.
- 95% of the crap people bring up from wrecks they would pass right over at a flea market.