>Please don't respond with something dumb like "you can stay alive without meat". Yes, we know that.

That part is actually the weakest part of your argument. You are dismissing a valid counterargument before addressing it.

Something being part of a current food production system does not make it a biological necessity. People can live without meat, therefore alfalfa is not "required for life" in the literal sense.

You are also shifting the meaning of "required": from "necessary for humans to survive" to "necessary for maintaining our current livestock industry." Those are very different claims.

Preemptively calling an obvious counterargument "dumb" is not a way to win the argument; it is a way to avoid having it.

Is it rational to dedicate enormous amounts of land, water, and energy to producing animal feed when those same resources could feed more people directly?

Using crops as feed and then eating the animals is an inherently inefficient way of converting resources into food. That may be acceptable when resources are abundant, but it becomes increasingly difficult to justify as we face limits in freshwater, arable land, and ecological capacity. That is the true argument, and what the discussion should be about, not if we can (very obviously) survive without meat.