They are a feature of civilization, not nature. Marking homosexual marriage as contrary to some natural laws is reminiscent of the justifications put forward in the U.S. for laws prohibiting interracial marriage. Moreover, all sorts of ideas about marriage have changed. Abraham ended up with a wife and a concubine, Jacob with two wives and two concubines. While surely not ideal, the rabbis of the age did not protest this use of marriage by one of their most revered teachers.
Families are always a subset of the society of which they are a part.
Marriage, likewise, is conditioned by the values and sensibilities of the social context. As society has come to understand the essential unchosen nature of same-sex desire, the offering of new forms of matrimony that support such couples would seem consonant with a contemporary sense of justice and social responsibility. Same-sex marriage, like marriage generally, is a conservative institution expressing lifelong commitment, caring, love and support. It is fundamentally not about rights, but about duties. Central to Orthodox Jewish teaching is the importance of family.