I think almost everyone can be reformed. I also know that some crimes won't have the option for parole . I'm ok with that. I think our prisons should be humane places.
For the average prisoner, I agree. People who steal, deal drugs, maybe even commit murder because of a crime of passion or getting caught up in gangs, the guy who date rapes once because he really didn't appreciate where the line was - I think all of these people can be reformed and should live in humane conditions.
Serial killers, serial rapists, sadists, repeat child sex offenders, criminal narcissists, repeat criminals with DSM5 Axis 2 diagnoses, etc. - I do not think they can be reformed. They are too twisted and addicted to their violent/abusive compulsions. One of my biggest faults is I lack compassion and forgiveness for these types of people and harbor only desire for revenge, severe punishment, and ache for them for the rest of their lives.