Whilst alone marriage is a mere social construct - it is something much more when you add children.
It's that commitment from and between the marriage partners and the children which is the foundation of human civilisation.
SSM devalues and trivializes that foundation.
Irrelevant in 2017 mate. Many people get married with no intention whatsoever to have children.
Couldn't I ask you the self same question with far more poignancy?
What?