Why do scuba divers hate spearfishermen?

I wouldn't say that's true of all scuba divers. I think there are a few divers who are spearfishermen. The rest don't necessarily hate spearfishermen, but they have totally different reasons for wanting to dive. The vast majority of divers want to enjoy the beauty of the fish, so they don't want to see someone killing fish and scaring the other fish away. It can be risky too, because bleeding and struggling fish tend to attract hungry sharks.