I'm not sure I would describe reading as a right as such but I definitely think it shouldn't be banned or be described as a privilege. I have problems with incarcerating people generally but if being in prison is considered to be a suitable punishment for your crime, then that should be that and you should be able to read if you want to. Withholding books as a privilege seems petty and an abuse of power - the prison service just humiliating prisoners because they can. I don't like bullying in any scenario and this seems like just another form of bullying to me.
Yes I agree, there is far too much abuse of power in gaols, hospitals, homes for the elderly, homes for abandoned or abused children. I mean it is not like there isn't an article a day in the newspapers etc. about abuse of power in some shape or form.
If your punishment for a crime (or perceived crime) is to have your freedom removed then that is enough. If my freedom was removed I wouldn't be interested in TV, books or anything else.
Don't worry about issues such as reading being a right or a privilege - worry about the people "in charge" of the persons encarcerated in such institutions and what they are up to - like sanctioned bullying.