Bleh. I agree with the sentiment, I don't agree with killing animals. But people are going to hunt and fish regardless, and a lot of good can come out of it as well, I'm not going to tell someone they shouldn't hunt or fish, it's just not for me.
If you actually care you should worry about tackling real issues, likes society's meat obsessiveness leading to factory farming, and commercial ocean fisheries. Both of which place large harvests well above animal welfare, and can be quite destructive to the environment.
Being a douche to some dude fishing with his family isn't going to make any meaningful difference in the world, and aggressive, confrontational tactics rarely achieve the desired result. Typically that type of behavior will only trigger backlash and draw divides.
I will say though that if someone is going to hunt or fish I hope they do so humanely and responsibly and kill the animal as quickly and painlessly as possible, not leaving a fish gasping for breath on the dock.