Sometimes there is, and sometimes there isn't. The law enforces a basic moral conduct built on consensus. That's what the law is. Sometimes, we legally enforce what people should do. Sometimes that's good, sometimes it's less than good. I agree with you.
There is a logical fallacy to your argument. You calim that you don't want to see a child lose the relationship he/she has with the only father he/she has ever known. But no law can ever force a someone to have a loving relationship with another person. So if a man finds out the child he thoought was his was fathered by another man, no law can prevent him from choosing to end the contact with the child. The only thing that the law can do is force him to pay money. So the law does not protect the child emotionally at all - it just protects the lying mother financially.
Sorry, they abolished slavery about 150 years agon in this county.