I cannot even wrap my brain around people who do this kind of stuff. I am certain they can't be 'cured'. You have to be a demented soul to inflict that kind of pain on an innocent being for no reason other than entertaining yourself. There are not even words.
We have a neighbor here that traps ferrals and has them fixed and released back here. She had like 20+ cats last I knew. I think she feeds them a minimal diet so they don't starve. She said they are not her pets though, she doesn't try to tame them or bring them inside, I don't blame her, there are just waaaay too many out this way.