I would say that some women are sterile and become mothers through adoption. And some fathers would share that solidarity. For me, it is about the shared experience of parenting. Or is a man who stay all night taking care of a sick child less worthy than a woman? Isn't his worry less than yours in a similar situation? If a woman can't breastfeed is less of a mother? If she adopts? For me, the core of the experience is about caring about your children, raising them, teaching them and letting them become their own person. And yes, part of than would be accepting who they really are, not just who we thought they would be. And for me it is implicit in loving someone. To see them as they are and accepting them fully, not projecting our ideas on them.