I think there are 3 main arguments for the imprisonment of criminals:
A) criminals can be locked away for a temporary or indefinite amount of time so they cannot commit another crime again
B) criminals in jail get reeducated, realize what they did was wrong and hopefully will not do it again
C) criminals in jail get punished for the crime, which in turn makes them and everyone else stay away from crime because they do not want to be subject to that kind of punishment.
And of course a person can agree to more than one of these arguments, especially since they are all interwoven. I would like to focus on people who are only supporting A and B, but not jail for the sake of punishment.
If there is a crime that can only be committed once, would people who do not support C make the criminal go to jail regardless of the reasoning behind A and B? Let's say a country has a monument and that monument has its own law against vandalism. The monument will not be rebuilt, meaning this law only covers the first person or group destroying the monument which in turn means that this law will be voided as soon as such event takes place.
Would you have to make the criminal go to jail under the reasoning of A and B?
(A) The criminal has never committed a crime before, he is not likely to cause further harm that could be prevented by locking them up.
(B) Teaching the criminal not to do that again is useless effort as this crime cannot be committed again.
The only real reason I can see them going to jail for is point (C) but some people are against this point.
To be fair this whole scenario is of very artificial nature but this thought experiment had me puzzled for the past hour