There are gay men who in times past would have married and had a family, now choose not to do so because they feel free to live life as they would rather it - this is true, and it's good.
There are women would have stayed in unhappy marriages in times past now have greater economic freedom and choose to not to stay in such a marriage - ditto.
yet they clearly also undermine the frequency and normativity of marriage - this is correct, although such number of cases wouldn't be large.
Gay marriage clearly destabilised the whole notion of what marriage and family are - no, I don't think so.
We've taken to gay marriage relatively smoothly. It was even a Tory PM who passed it through Parliament.
I think something else has been used to attack the traditional family.