Isn't freedom important for human dignity?
According to the standard moral doctrine it's not as central as bodily integrity. The state is allowed to take away freedom of movement but not bodily integrity or force people to work as slaves.
Also, remember that prisoners are often subject to beatings and rape by other prisoners or guards--something which is widely known.
That's a feature of the particular way a prison is run.
According to the standard moral doctrine
There is a "standard moral doctrine"??
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.