It’s well-known that when you put people in a position of power over others, some of them will abuse that power. There are ways to try to minimize this effect, for instance by dividing power or multiplying means of supervision or surveillance — but there’s no way to avoid it entirely. If enough cops pull over enough people, odds are one of them is going to take advantage of someone sooner or later, no matter what evaluation or management procedures are in place. The same goes for every situation where there’s a power differential. You can hope that the people in power will be good and responsible, and you can do as much as possible to make sure that only good and responsible people are selected for the job or that the structure of the institution incentivizes good and responsible people — but at the end of the day, people are people, and abuse of power is all but inevitable.
With this knowledge in hand, the model of the patriarchal family makes absolutely no sense. There are no real qualifications for becoming the father other than a functioning reproductive system. There is no effective oversight of what goes on within the private sphere of the home — indeed, the privacy of family life is one of the most treasured values. And the people subjected to the near-absolute power of the father are precisely the most vulnerable people in any society: children. What could go wrong?
Modern society has certainly tweaked with the traditional model to a significant extent, relying primarily on the willingness of the mother to leave an abusive situation and take the kids with her. In extreme situations, the state itself will intervene to take the kids away from an abusive parent’s custody. Yet the primary strategy is to provide exit strategies for when things go wrong. And of course conservatives are constantly fighting to make those exit strategies more difficult — and to cut off the means to avoid becoming entrapped in bad situations in the first place (i.e., birth control and abortion).
This is where gay marriage is absolutely necessary: at its best, it provides a model for a voluntary union of equals. Unless we’re going to go the full Republic route, it seems that more or less autonomous households are here to stay — and so we might as well have them forming without all the baggage of patriarchal presuppositions. This is the good way that gay marriage challenges the traditional family: by pushing it further in the direction of being a realm of love and affinity rather than a regime of property.
Obviously this isn’t a magic-bullet solution, because gay marriage and the changed marriage norms it can hopefully bring with it do not lead automatically to a utopia in which everyone is good and responsible. Yet the patriarchal model is practically begging the father to abuse his power, and so moving away from it can only be good.
Thus I would say that straight people would do well to make their marriages a little more gay.