I think its a matter of common sence and discrestion. Keeping stock trout dosn't bother me, especially if the lake dosn't hold them over well. I agree about walleyes, but many slot limits already address these issues. Panfish I harvest readily. Certainly large breeding females during spawn time.
You have to take in consideraton the species and its current status in a body of water. I have fished many tiny brook trout streams that needed a harvest of fish. I also fish a reservoir here in MA that had an overpopulation of lake trout and F & G was encouraging folks to harvest the fish by increasing bag limits and reducing size restrictions.