I don't think that it has to be a black or white issue. Some people likely cannot be rehabilitated because they are psychopaths, some because they are simply evil, etc. However, that doesn't mean that there are not many people who could be reformed.

For example, John Newton was a slave trader before finding God, becoming an abolitionist, and writing "Amazing Grace".

The Apostle Paul was at least an accessory to murder before his conversion.

I'm sure that there are examples outside of Christianity. That's just my background so its what I know.