Complementarity is a reality that God printed on our bodies, completed only with our Yes and our compliance to His will for us.

He did this so that we wouldn't forget that we were made for unity, eventually total unity with Him. 

It's a gift from God.  A grace.  

A yes that often leads to new life.  If we close ourself off to God's gift, by denying our own God-given capacities, by denying life, by "splitting the gift", then we deliberately add "disunity" into not just our relationship with God - which is most important - but in our relationship with our wife. 

And even more so with other unnatural couplings, which can never lead to new life.