In the U.S., some 41% of children are born to single mothers. Our custody laws assume all children to have been born to a married couple. That means stark inequalities between unmarried mothers and fathers. In every state, mothers have parental rights solely by virtue of their biological connection to their children. Fathers have a biological connection too, but must spend significant sums of money and jump through various legal hoops in order to establish their rights.
Combine all that with the fact that, although we have, for the first time in human history, the ability to know to a certainty the father of every child, no state performs genetic testing on every child when it’s born. Some 30 different tests are performed on newborns, but not the one that would benefit dads.