In order to accomplish gay marriage, the debate has changed the subject from the imposition of obligations to the granting of rights. This reversal has been immensely successful in making the argument that gays should be granted the same rights as heteros. In fact, its been so successful the religious right has engaged in accepting the premise and has also been suckered into it.
However, the redefining of the reason for state involvement has a dangerous and is eventually lethal to the concept of the obligations of marriage. Because marriage will be heretofore a concept that grants rights to the parties and not obligations, the laws and the court orders will begin to reflect this change. Spouses that get abandoned will not get as much support from the state as before.
This will be enhanced by the existence of the precedence of cases which gays will be bring forth. Their cases will be mostly concerned with dividing property and most likely determining who by virtue of having earned the property are most entitled to it. The result of this is we will move farther away from the concept that spouses are responsible for the children and their spouse if a marriage terminates. In short, the losers will be the the weakest members of the family and by extension the society as a whole which will be forced to pick up the pieces.