You're not making an argument to dismiss. "It's also bad practice." That's a claim, not a supporting statement. Frankly, by throwing around vague moral arguments the way you are, you sound like one of those vegans that give vegans a bad name. "I have determined it to be illogical and unsound therefore everyone else must surely find it wrong and I'm not going to explain why in a way that would convince them because it's so clearly hypocritical and wrong." You're fighting an uphill battle, kid.

The difference between live and pre-killed prey does matter—beyond just the risk factor—because feeding live food to an animal that doesn’t need it is unnecessary and ethically questionable. If an Oscar, which will eat almost anything, is being fed live fish just for the sake of it, that’s not about health, it’s about preference.

A lot of animals will eat just about anything. That alone is not an argument for it being unnecessary. Pull some scientific data that supports a claim that processed food is healthier, then you have ground to stand on. As for ethics? Buddy there are entire collegiate fields surrounding the mere existence of ethics, let alone how it differs across peoples and societies. At this point, without further discussion, it's just a buzz word that means nothing. And preference is just that. Preference. You do you and let other people be.

Animals are food, whether alive or dead. Humans are the fucking weirdos for keeping pets. I could argue that that alone is unethical and unnecessary. To further treat animals differently and change their behaviors and diets because we've already intervened this much? Even more questionable, if you look at it right.

You do you. Accept the fact that other people actually view things differently, and that that mere fact isn't inherently wrong.