If the nuclear family is a human good worth protecting, it is the responsibility of all members of society to do so, including homosexual members of the community. An extension of this is upholding the institution of marriage as between and man and a woman. This does not imply repudiating their own committed unions, nor where the exigencies of life require it, raising children.
Dover Beach, the poem by Matthew Arnold.
Update: 1. Why SSM has to be seen as a part of a larger agenda. h/t Snoopy in comments.
2. How many SS couples wanted SSM before it became an identity issue and a part of the larger agenda?
3. How many SS couples are suffering for want of SSM in the way that people are suffering from many other things, including lack of free speech, that have been starved of political oxygen by the division of the non-left forces due to this distraction?