"Why is it reasonable to believe in prisons, but not in the hell?"

[FlatAssembler]

You're still bickering over hells relative injustice as though that mattered to the claim that hell is necessary to justice.

The harm that something does influences the a-priori probability of it being necessary. Saying that grass-fed cows may be necessary to feed growing population, in spite of the harm they do (methane emissions...), is a-priori plausible, since the harm they do has relatively little with our ability to produce food. Furthermore, maybe there is some truth to the claim that a grain-based diet will lead to soil depletion. Saying factory-farmed grain-fed livestock is necessary to feed growing population is much less plausible: it is taking food away from us, rather than giving it to us. And if grain-based diet leads to soil depletion, factory-farmed livestock obviously makes things even worse. But saying factory farmed livestock is necessary to feed humans is still more plausible than saying that hell, which is an infinite injustice, is somehow necessary for justice.