They are hoping that the court will adopt their view.
My point was, if you take this view of marriage-that it is a personal choice like steak tips instead of brisket, and that it affects only individuals (which, BTW, no society anywhere at any time has ever done)-then the plaintiffs have a good argument.
Another way to put this is that, if you allow heterosexuals to have "gay marriage" (unilateral termination at will, multiple albeit sequential partners, no commitment to reproduce, and lots of governemnt benefits to define the relationship), then the case to deny "gay marriage" to gays becomes quite weak.