Why shouldn't repeat rapists have their surgically removed?

I say first time rapists get long prison sentences, and if they do it again after release, they have their genitcals removed. The only reason why they should get 2 strikes is because a possible miscarriage of justice. Don't you think re-offending -offenders should have their removed? Let's face it, they WON'T do it again, and if they do and get caught, their uality is screwed up, it will make them think twice.