Very interesting topic! For me, when I take in a fish as a pet, I am depriving it of a natural life in the wild. So I take it as my responsibly to reasonably ensure a good quality of life. That means keeping the fish in a semblance of it's natural environment, with reasonable space, food, etc. It's life doesn't have to be perfect, since life in the wild is far from it, but my goal is to provide a better than average quality of life for my fish, to justify pulling them out of the wild for my own entertainment.
As far as feeders go, being eaten is part of life, so I have no qualms with feeding fish to fish. However, I think they should be treated well until they are reading to be fed. So it's unfortunate that all those feeder goldfish, etc live in poor conditions prior to being sold.
For sport fishing, my personal opinion is that as long as my intent is to eat a suitable fish, it's okay for me
I'm not too enthusiastic about the idea of fishing for the sake of having fun. A caught and released fish is certainly going to be injured, and in pain and shock. If I were a fish, I wouldn't want a hook through my jaw for "sport". So when I fish, I do it with the intent of feeding myself, not simply for entertainment.
So basically, as long as it's in line with the course of nature, I'm good with it. Life and death is natural, and animals need to eat to survive, as do humans. However, since humans are unique in keeping "pets", we need to make sure we are not causing unnecessary harm to the environment, or suffering to the animals under our care and protection. JMO.
--Adeeb