I tried to argue this once and had people claim men get custody a lot, too. Then you look deeper in the cases where men get it and its almost always special cases where the mother is beyond unfit. And even then there's tons who are horrible mothers and did not lose custody. Women have it the easiest in custody battles, you could just claim the father hit the kids. Just a superficial glance can tell you women win most of the time and a deeper look into will show that even horrible women win and very, very rarely lose.