Can you imagine how nasty those battles are going to get with this sort of law in place?
One of my friends ex-husbands can already get the cops to raid her house every few months if she pisses him off. They have to do it because he says she is hurting the child and they have to check it out.
Now he can ge her declared a sex offender as well. Sure she can do it back, but he can afford the better lawyers and would probably win.