I was thinking whether, considering the nature of the wizarding world, Azkaban is really that unreasonable a punishment for Death Eaters. Keep in mind that in order to deter crime (to acausally prevent it) a potential criminal calculating the expected utility of committing a crime must get a negative value.

This value depends on:

• EB, the criminal's expected benefit from getting away with it.

• SP, the severity of the punishment should he get caught.

• p, the probability of getting caught.

Specifically we want (1-p)×EB < p×SP or equivalently (1/p-1)×EB < SP.

In this case the expected benefit of successfully taking over the government and establishing a dictatorship is quite high. Also the Death Eaters were only stopped by a complete stroke of luck, so p is quite small. This suggests we need a very sever punishment to deter would be dark lords and their minions.

The punishment needs to be so sever that even though the would be dark lord and his minions have a good chance of succeeding, they're still deterred because of how severe the punishment would be on the off chance that they fail.

Given this, condemning them to spend the rest of their lives being tortured by dementors sounds about right.