Only if you think that it's a sex crime. It's a power crime - the offender has power over his victim. You don't need testicles for that, or ovaries for that matter. You need a functioning brain, and a way to exert power. Castrate him, and he is still capable of thought, he still has hands, and he can still speak. He's still a danger. As long as he can think, he's capable of the motivation. It's not like neutering a cat so he doesn't spray, or having your dog fixed so he doesn't wander. Kill him, and you remove any chance of him ever doing it again.
Excellent post!
Actually, the power can be wielded in non sexual ways as well. Sexual control/power is a major contributor to these folks motivation to commit the acts. There is a reason eunichs were made eunichs. Castration may actually simply remove the motivation to exert such power as much as taking away ones Harley Davidson removes their desire to buy chrome accessories.