It threatens the institution of marriage. It gives out the message that the primary purpose of marriage is sexual satisfaction and that procreation is now merely an option to be taken up by those who desire to have a child or children. It is an attempt to overturn the long held Judeo-Christian concepts of marriage, love and family by confusing 'agape' and 'eros'.
The Church is seemingly powerless to prevent the advance of secular mores which contradict the Divine Will but there is every reason that it should try to for the sake of souls, lest its failure to do so be construed as condonance.