I agree in theory that nature is brutal, we raise cute animals like chickens, pigs and cows for the sole purpose of eating them, and there's some hypocrisy in gleefully raising some creatures to eat or to feed to others, while drawing a line in the sand at other animals for emotional reasons. I can't find a logical, sound argument against someone doing that, while also buying daphnia to feed to my fish alive, and even enjoying watching them hunt them down, since my fish get so active and excited, and I know that the live food is healthy for them. So, I am a hypocrite.
But I would still look askance at someone raising bettas solely as food
I agree with culling deformed or unhealthy fry when breeding fish. It isn't good for the fish to allow unhealthy fry to survive and pass on those genes. But I don't keep predatory fish, and my version of culling is moving them to a female or male only tank to live out their lives with me. But I'm not producing hundreds upon hundreds of fish (well, 2-3 hundred), and have only had a handful of deformities. Someone breeding angels for example would soon run out of space if they kept every cull, they can't be housed in big groups like my guppies throughout their life. The reality is that they have to cull hard, and they can't possibly keep all of them. I think better that they keep the circle of life going and feed a predator fish that will benefit, than to let a deformed fish suffer a short unhealthy life, or give them to someone who might breed them, bringing down the health of the captive trade angels overall. I find the practice of breeding animals that have deformities much more offensive than feeding a carnivore live prey.
I even encourage people who keep livebearers and don't want to be overwhelmed with fry to leave them in a community tank, and let nature take its course. But I also advise to give some hiding places like plants to give the strongest, healthiest fry the best chance of making it, it's how the 55 community tank here is run, and soooo many fry survive. The fry in my tanks remain with the adults until their large enough/there are enough of them to move them to the grow out tank, so I know some must get eaten, and I could catch them all as newborns to prevent that, yet don't, so they cull them naturally.
I don't keep snakes, but I watch Snake Discovery, and like snakes, and know they need to eat. I kept pet rats as a kid and love them, I know they're pretty intelligent, sweet, playful animals. But they're also a part of the food chain, and a natural, healthy food for snakes - but don't agree with them being fed live unless absolutely necessary. Yet I have no problem with a snake keeper breeding rats for the purpose of snake food. And how is that different than raising bettas for that? It really isn't, I just don't like it from an emotional level, and couldn't do it myself, just like I couldn't euthanise my deformed but otherwise functionally healthy guppies.
I guess the difference for me, is breeding rats humanely for the purpose of food, humanely euthanising them before feeding, and doing it because it's necessary, is different from gleefully taking joy in breeding bettas for the same reasons. Sorry for the messy, disjointed essay, I guess my thoughts are too conflicted to make a logical argument either way. It's just my opinions.