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

[The Grand Nudger]

it's not authoritarianism to suggest that some crimes are committed by people who simply don't know any better or have nothing better.

Then what is authoritarianism? And why punishing adultery with prison would not be authoritarianism? That is what you are suggesting, right? If you ask me, such a suggestion has far less merit than the suggestion that people should be thrown into jail for eating meat.

We don't throw people in jail for cheating on their spouses, but, no..simply having such a law would not make a system or ideology authoritarian.  

They didn't have the benefit of hindsight as you and I do now, and that certainly wasn't their expectation.

I am not sure what you mean? What was their expectation? That they will be remembered as heroes for joining an illegal army that attacked a hospital? Makes zero sense.

People can be informed by rational but inaccurate expectations.  Most soldiers, on either side, imagine themselves to be the heroes of the story.  To say that a decision is rational is not to say that it is the good coarse of action or the best coarse of action or that all relevant facts are accurately apprehended by the decision maker.  

A thing being bad does not suggest imply or demonstrate that it does not exist.

Sure. But prisons existing would contradict the Principle of Rationality. Massacres and terrorist attacks happening does not contradict the Principle of Rationality because it does not require any group of people to be systemically biased. In massacres, it does not matter that most soldiers desert, as long as there are some soldiers who do not desert, a massacre will happen. But prisons existing requires politicians to be systemically biased towards believing prisons should exist.

No, prisons existing doesn't contradict the principle of rationality.  If people feel that prisons are an adequate course of action with respect to some objective, then there will be prisons - this is what the principle of rationality states.  This is what we see in the world.  Insomuch as they deem it inadequate or inappropriate, they will lose faith in the institution itself and whatever body maintains it. Also what we see in the world.

Your argument takes the form of a pretty standard non sequitur - an appeal to consequences. If this were true, that would be bad, therefore it's not true.  Perhaps prisons are bad, but to conclude that this means that there are no prisons is irrational - whereas a different conclusion - that we should take control of the prisons and reduce them to rubble - is rational. Similarly, "if these people existed, that would be bad, therefore they don't exist" is irrational. "If these people existed, that would be bad, so we should kill them"...rational.

Rationality implies the conformity of one's beliefs with one's reasons to believe, and of one's actions with one's reasons for action. "Rationality" has different specialized meanings in philosophy, economics, sociology, psychology, evolutionary biology, game theory and political science.

It's rare that a short and simple definition clears up so many misconceptions at once, but can you see how it answers your questions? Let's extend it one further. For some people, a belief in hell would be just as rational as a belief in prisons. There are people in the world who's beliefs about hell match their reasons for belief, and in the case of evangelists (for example) where their actions also match.