Of course castration is perfectly normal. We do it to livestock all the time. And what's the problem with taking a muscle out of your forearm and shaping it like something that isn't real? When they can change XY to XX or XX to XY, boy won't THAT be something!
Yeah, but never take it away entirely. Children shouldn't be allowed to do things like that. The minimum age could be 25 (When the brain has fully developed and can make appropriate decisions)
To be honest, I don't think the brain has fully developed if one considers hacking away at their genitalia because they believe it will affirm what gender they believe themselves to be.
But, if they are an adult, their decision...my opinion.