I know that you may feel that a person's sexual predilections have no bearing on their psyche... Obviously, the government does care. Otherwise there wouldn't be any concerns over pedophilia or beastiality, or even someone's sexual offense history (exposers, violent sex, mutilators, or those who have raped women). Now before people start suggesting I'm equating sexuals with those in that group; I'm simply explaining why your argument that the state shouldn't care what people do in bed is not completely sound...
Maybe you meant that people shouldn't care about what two consenting adults do in bed... that's probably a better arguement... Children are a third party in that scenario however... Obviously if a child reared under two sexuals also became a sexual why would society consider that a detriment? After all, if sexuality was deemed as perfectly 'normal' behavior why would that child's sexual preference be deemed abnormal? That's the slippery slope no one seems to care about...