[graemep]

As I said in another comment this leads to many people being disadvantaged.

I do not know where you live, and these laws vary between countries, but in the UK marriage gives you a lot of important legal rights. Not marring disadvantages a lower earning partner (most often a woman who has taken time off a career to look after kids) if the relationship breaks down, it does not give you the same legal rights if one dies with regard to inheritance (no real rights if there is no will, far less right to contest a will, and the loss of a significant inheritance tax exemption even if there is), or being automatically next of kin (I think this has improved in practice), no automatic joint parental responsibility for children, etc.