The history of recent social reform is littered with forgotten assurances and moved goal posts. As soon as the legislation for same-sex marriage is passed, the liberal left will look around for new causes to pursue.
Inevitably, this will involve seeking to overturn some still surviving aspect of our Judeo-Christian moral and cultural heritage. Obvious targets include polygamy and lowering the age of consent.
Groups of polyamorists will be wheeled out, demanding an end to discrimination against their lifestyle. Polyamory is very much a niche way of life. The real beneficiaries, when the legislation is inevitably passed, will be Muslim men, who will be able to legally have multiple wives.
The liberal left does not grasp that value systems are in competition. Both the traditional Judeo-Christian moral system and Islam are viable; they would not have stood the test of time otherwise. The liberal left world view is not, for the simple reasons that it undermines moral values and leads to sub-replacement fertility. It is time to start rebuilding our Judeo-Christian moral outlook – the alternatives are worse.