Absolutely. And in prison it should be easier to verify that they vote just once

This is like requiring a stranger that attempted to break into your house be forcibly allowed on your property later against your wishes (assuming you rationally consider such a person untrustworthy and no mitigating circumstances or other data exists that would make you consider them trustworthy)

It's not like that at all! There's no right to enter a stranger's house in the first place.