sportfishing and spearfishing have pretty low, even non-existent, by-catch rates. To me, seeing the guy fishing off the back of the boat is better than serving fish on the boat that was caught with a long line, gillnet, drift net, bottom trawl, etc. The fishing that goes on where you can't see it is often a lot worse than the fishing you can see.
I can imagine a vegan asking a similar question, and being disgusted that divers are eating fish at all.
I'm not a vegan. I still eat everything, and even fish.
Anybody see the images from Brian Skerry in a recent National Geographic? check out the shrimp bycatch photos in particular, the first and the last:
http://www7.nationalgeographic.com/ngm/070...1/gallery4.html
http://www7.nationalgeographic.com/ngm/070...1/gallery5.html
http://www7.nationalgeographic.com/ngm/070...1/gallery9.html
http://www7.nationalgeographic.com/ngm/070.../gallery13.html