Spearfishing is the most ecologically sound way of harvesting fish from the ocean.
There is no by-catch.
Illegal and undersized fish are not taken by mistake.
Fish are killed quickly rather than suffocating to death.
It is the responsibility of the spearfisher to make every shot count, to make every attempt to keep a fish once speared, and to take only what they will eat. Protection of the ocean's resources is of the highest importance.
It goes without saying that you should follow your state rules and regulations concerning fish and wildlife. Furthermore, the responsible spearfisher limits his catches. Even though it may be legal to take 15 rockfish, the number taken should be dependent on the number of fish in the community. Taking one fish per reef or school is a good guideline to follow.
In the ocean, big fish eat little fish. Nearly every fish in the ocean will die a violent death to feed something larger. This is the normal, natural life of a fish. What is abnormal for a fish is to have itself and every other fish in its school scooped up in a net, thrown on a deck, and die by either being crushed to death by the weight of its brothers and sisters above it, or by suffocating out of the water.
Spearfishing is selective, ecologically responsible, and honorable. Compared to commercial fishing, I think the fish would see it that way, too.