Malcolm wrote: There is no justifiable argument that can be produced which can show that gay marriage is disadvantageous to society as a whole.
At least nothing we can discern at the moment. The future will tell.
As I said, recognizing gay marriage sets a legal precedent for any other unrecognized group seeking legal sanction for their presently unrecognized activities. This means advocates for child marriage amongst some minorities in the west will have another precedent to refer to as far as legal matters go. One could say gay marriage is a separate issue as it concerns consenting adults, but it is a human rights issue and child marriage proponents could likewise argue their own human rights are being infringed upon in a similar fashion.
Have you checked the divorce rate lately?
There are many factors at work behind this trend. Consumerism, popular feminist values and lack of community expectations are all contributing to divorce rates being so high in the US and elsewhere.
In stabler social arrangements of past times divorce was not such an issue. This is observable in plenty of places in the world where divorce is not so common even when women and men alike have the right to initiate divorce, though in my estimation social norms and community expectations likely often force many families to stay together, which is in the long-term healthier for children.
Actually popular feminist values likely prompted the increase in divorce over the last few decades. This was perhaps another unforeseen consequence of rapid reforms. This is why a cautious albeit generally tolerant, conservative approach has many advantages rather than rushing through changes and attempting to stamp out disagreement.