Rehabilitating someone with "radical" ideas would involve acknowledging and challenging their ideas. That's not how rehabilitation really works even in theory - most rehabilitation is taking criminals who aren't ideologically motivated and solving the much simpler problems of educating them so that they can work.
Reading this, I'd bet £1000 to spat out sweet you are US-American?
Because elsewhere, most of the civilised world treats prison as rehabilitation.
I look with envy at how they do a lot of things.
I would assume that rehabilitation does not focus on changing people's ideological values.
Am I wrong? Is that a thing in other countries?
Few countries in Western and/or Northern Europe? That's a very narrow definition.
* Retribution ("a punishment")
* General prevention ("a jailed person cannot keep hurting others and prison threat is a deterrent")
* Special prevention (rehabilitation)
Last time I looked, most countries are mostly for general prevention with a pinch of special prevention. Retribution is not currently defensible philosofically or technically, though some people errounesly think it's the basis of the system.
Even without the spelling or the previous reference to GBP, I could have guessed nationality from your tone.