Arguing the importance of social networks: "Married people were indeed healthier - if they weren't lonely in their marriages. If they were, the health benefits were so negligible the researchers considered them statistically insignificant."
Andrew Sullivan asks an interesting question as to why gays want to marry considering they have been politically and socially excluded for their sexuality. He takes a conservative view that it the gay community's desire for conservative values.

As someone who is going through a dragged out divorce which is still not settled despite being fourteen months since the separation I can honestly say I will get married again. My partner asked me this morning why I would want to given the hassles the divorce has put me through.

It is probably for the same reason the gay community does. Marriage is a universally recognized social convention that is a public declaration of love, commitment and devotion to your partner. It has transcended the religious and political basis for it simply because it so recognized as a convention.

If another more powerful convention came by which people could declare and re-affirm their love for each other then I imagine marriage would become a minority ceremony only practiced by certain denominations. But there isn't, so marriage is it.

Like I said, I am sure I will get married again. The divorce process, while emotionally difficult, has not left me with burnt fingers. It is still a good institution by which to publicly announce and affirm your love and devotion to your partner.
Karine Lamiraud and Henry Saffer look at social interaction:

Marriage tends to reduce all social interactions, which suggests that a spouse is a substitute for other social interactions.

Your wife is generally not only your lover but your best friend as well. You are actually spending your time in a very intimate friendship when married. The 'substitute for other social interactions' kind of misses that point. In my opinion, and as someone going through divorce, this is why separation and divorce are so distressing: you are effectively losing your lover and best friend when a marriage falls apart.
Cam Riley: South Sea Republic. Freedom, liberty, equity and an Australian Republic.