We are discussing sexual behavior. Many of the laws are rooted in morality. Protection of person, protection of property, honoring contracts etc.
Recognizing the right of a person to choose how and whom they has sex with does not make the law amooral. It makes it the responsibility of the citizenry to be moral. Some will and some won't and some will define there morality differently than you and I.
I don't need the law to protect me from two guys on the next street having sex. Why do you?
All laws are rooted in morality.
Morality comes from a priori assumptions at bottom. What you think is moral or immoral may not be co-extensive with someone elses. To suggest that those with different a priori assumptions are nutters is really quite intolerant, at least up to a point.