Why fish for salmon in rivers? Historically it was for food. people used nets, spears, boards and woven baskets among other means, also there are artifacts of carved bone fish hooks and woven lines. I'm not going to type the entire history of salmon fishing in the world and a history of fly fishing for salmon because you can research that yourself.
Why do you fish for salmon? Personally I fish for salmon for food. IF its chrome take it home, if it's black put it back.
Any spawning salmon are not chrome, so by logical deduction I am fishing the run and not the spawn. Wild kings on our end of the lake are incidental catches of people targeting lake run browns, which enter around the same time in late summer and later while fishing the steelhead run.
Coho`s early are tasty and targetable and not very easy to catch again many are caught incidentally fishing for steelhead and runs are wild and still plentiful on our end of the lake.
In a way its novelty because, a meal of sunfish and walleye is much easier to catch and way more plentiful but a coho or fresh king on the grill is nice once a year, pretty clean on our side of the lake, better check the fish advisories for your areas and rivers.
Salmon are not supposed to be here at all, stocking stopped many years ago, pinks were the result accidental dumping, cohos were stopped in the late 70`s and Atlantics and kings in the 90`s.
All in all the salmon, browns, brooks and steelhead seemed to have struck a balance, I dont think the salmon are ever going away completely they are making it on their own.
Is it ethical to fish for salmon that cant reproduce or shouldn't be there in the first place even if they do reproduce? That is entirely up to you, but personally I do not cast to anything on the redds or sight fish, not even sunfish. Get there before they spawn.