I’d oppose it for this reason and because it seems cruel and unusual to me, especially if it doesn’t even make a difference in the outcome. But even if it did, I care too much about bodily autonomy to be okay with this.
Sounds like ‘Cruel and Unusual Punishment’ to me. Not only odd, but ineffective. It’s their warped brains and their legs that make rape possible, not semen. There isn’t one serial rapist without legs, but if one was castrated you now have a potential rapist who DOESN’T leave evidence behind.
Much of it comes from having exhausted all the typical kinds of hedonism so they need more extreme and depraved acts to get the same pleasure. You typically see this with porn addicts. Many people basically turn into real life Cenobites because nothing else feels the same any longer.