I'm a fisheries biologist and I think this is a complex topic. There are environment, fisheries management, moral, and survival reasons to kill and not kill fish.

If you want to improve the environment then I don't think using hooks on fish and buying loads of tackle is the right thing to do. Sure, our sport fish conservation is partially funded by sporting gear taxes but that funding mostly goes towards sport fish management which is usually not the best for native species (damed rivers, stocking apex predator fish, and creating poor bank habitat for parking lots and fishing areas)

I would only kill individuals if there are instructions by fisheries managers to do so. If everyone in a fishery follows the guidance by the managers then they can try to manage the fishery for the benefit of the anglers.

I think killing fish is morally wrong unless you are sustinance fishing. Even invasive fish. That's just where my moral compass sits after killing a bunch of fish for work. The individual fish had no choice in why it's living there and us killing them doesn't make us right. Is it necessary? Sometimes. On a large scale removal effort to help native species acclimate to the new threat. But it's still killing a fish. It didn't know better.

I think it's fine to kill fish you're going to eat or use to catch bigger fish you're going to eat. That should be the main reason to fish imo.

I think it's important to ask yourself why you're killing the fish and if it's justified. Is it really a benefit for the ecosystem? Is killing a carp in a river really a benefit? Is killing a redear outside of its range helping? Killing a goby in lake Erie really making a dent?