but in reality, it is nature.
but it really isnt, keeping fish in an aquarium in a country that they shouldnt "naturally" be in isnt natural, breeding fish so that they have desirable characteristics like ling flowing fins or specific colours isnt natural.
Also, in the wild fish that could be classed as food to some fish actually have a chance of getting away, in someone 4x2x2 tank at home there isnt anywhere for them to go and run away.
Personally i think in the majority of cases feeder fish can be unnecessary, and i think most predatory fish can be trained off live feeders if they dont take it at first.
I apologise to use someone as an example but in the profile in the tff index of the frogmouth catfish (or the chaca chaca) cfc says that it was one of the only fish that he couldnt convert to frozen foods. Fair enough, he has had to feed a couple of all the fish hes ever had feeder fish, but imagine how many predatory fish hes had in that time, a few is hardly any at all, especially considering the fish that he keeps are the ones that are considered to "need" feeder fish a few is hardly any and to the average FW fishkeeper i would be suprised if they kept one or two fish that actually needed feeder fish in their whole lifetime.