It's not necessary to employ a new ethical principle of physical integrity or bodily autonomy. The reason it's wrong to hold down a newborn boy and rip, tear, cut, and/or suck his penis is because these tampering with the genitals of a child is child molestation (by definition), and the perpetrator is a child molester. Does a child have the right to virginity? Does an adult have a right to not be sexually attacked with a knife? Yes and yes.
A child molester who is told "no, you may not molest my son" might indeed suffer from being unable to indulge in their lust for violence. However, it is pathological empathy for child rapists, not compassion, to refuse to name this crime of child sex abuse.