[bdowling]

> other than a pure appeal to morality.

There are several reasons to imprison criminals:

(1) To physically prevent them from harming the public again.

(2) To discourage them from committing crimes again in the future.

(3) To punish them because punishing criminals is morally just.

Reasons (1) and (2) are what you are thinking of when you say it’s useless to keep an 88-year-old in prison. (3) is your “appeal to morality”. However, there is also:

(4) To discourage others from committing similar crimes.

That last reason is just as important as the others, if not more so.