Maybe we could look at forced and irreversible sterilisation of rapists too.
Happy, sterilising rapists wouldn't make the slightest difference. That just means they cannot make their victims pregnant. I suspect you mean castration, which I'd also contend would be ineffective.
Rape is much less about the sexual urge and much more about violence and control.
I agree with the suggestion that prison is usually unproductive, but it's what the majority of the population demand, and our politicians are too populist and/or apathetic to seriously look at alternatives.
One process which has been shown to have some positive results (though not in every instance) is victim-offender conferencing, where the parties meet in a suitably supervised situation and the victim explains in detail the effect the crime has had on their lives. Now, of course some criminals will just shrug their shoulders, but others will for the first time consider the effects of their actions.
That prison doesn't work can be shown by the high rates of recidivism, especially if the offending begins in a very young person.
Removing serious offenders from society is often going to be necessary, but it needs to be accompanied by some constructive programmes.
I remember reading an article a while back about a group of violent young offenders, jailed, who were given the responsibility of looking after an abused dog. It was their job to physically care for the dog, and to find ways of restoring the canine's confidence in human beings. They initially scoffed at such an idea, but when actually experiencing the presence of the dog, they quickly responded and the outcome was very good, for the offenders and the dog.
Maybe such programmes as having the responsibility of planning and caring for a prison garden which has to supply the vegetables for the inmates would be useful.
I may be quite wrong, but I think when people undertake responsibility for achieving a given outcome, they usually rise to the challenge.
Just sitting in a fairly comfortable jail cell with all meals, laundry, exercise, etc planned and provided can't be conducive to any improvement in self worth or optimism for the future.