An important reason for legalizing gay marriage can be found in the nature of marriage itself. What truly differentiates civil marriage from other contractual relationships is not "one man, one woman" as conservative Christians claim, but fact that it establishes, legally, socially, and morally, a new kinship — and by extension, a new family. This, more than the legal rights which come with marriage, is why gays demand and deserve marriage equality.
Why is the “next of kin” the spouse when we have a stronger biological relationship with parents or children? A stronger biological relationship isn’t the same as a stronger kinship relationship. The relationship with a spouse is a chosen: you can’t choose your parents or siblings, but you do choose your spouse. When you choose a spouse, you are doing much more than moving in with someone. However much a cohabiting couple may love each other and however long they may have been together, they are not “kin” and cannot make any legal, social, or moral claims on others to treat them individually and jointly as if they were.
The only natural kinship ties are biological, and the only obvious biological kinship is that between a mother and child; all other kinship ties are created by culture and religion. Kinship is thus an amorphous product of other institutions which help people structure their relationships with one another. The importance of kinship as a means for structuring relationships and behavior is demonstrated by the many formal and informal systems for establishing pseudo-kinship between people who have no biological relationship and for whom there are no means for creating traditional kinship ties.
Heterosexual couples have the option to establish kinship by marrying. Homosexual couples, whose love and intimacy are no less valuable or significant have been unjustly denied the ability form a kinship bond with one another and this puts their relationships at a disadvantage. It's only natural that gay couples, whose love and relationships are no less deep and enduring as a those of straight couples, would want to become recognized as kin, thus creating a new relationship and new ties not otherwise available.
Yes, gays are asking others to recognize their relationships as kinship. There is no good reason why they shouldn’t. There is nothing about the relationships of straight couples which makes them more worthy of the legal, social, and moral obligations traditionally structured as marriage.