Brain Fertilizer

You may be right, though I'd rather argue the principle if I have to argue at all. Marriage is all about the fact humanity is made up of two sexes, and the formal mating arrangement, for sound social reasons, needs to be limited to one of each sex.

Eliminate that factor, and there really is no logical reason not to recognize marriages involving more than two partners. The main argument against this "slippery slope" observation is almost always, "Society can say no to polygamy if it wants to," yet the logic for preventing the recognition of polygamy by saying no to same-sex marriage is much, much stronger.

Further thoughts: it's been argued that same-sex marriage should be accepted because marriage is about love. In particular the argument is focusing on intimate love -- which is by definition not a social matter.

Marriage is a social institution because there are social issues that it is designed to regulate. Intimate love is associated with the relationships sanctioned by marriage in most (by no means all) cases, but that is not why marriage has become a social institution.

Reducing marriage to being about intimate love is in effect a denial that it is legitimately a social institution, an attempt, whether by accident or design, to eliminate marriage as a social institution altogether. To make it purely an intimate matter and to set the social consequences of the relationships in question adrift without established social remedies.

The breakdown of families is a consequence of the weakening of marriage over the last few decades. It is unreasonable to argue that further weakening marriage will not result in more negative consequences.

Actually, I'd think that cohabitating heterosexuals would be more likely to push for civil unions, with the assumption that civil unions would be available to opposite-sex couples as well as same-sex couples.

That's certainly what's happened in Canada - common law marriage was greatly enhanced (in both priviliges and legal responsibilities) and extended to same-sex couples. After that, the number of opposite-sex common law marriages skyrocketed.

It seems to me that the only way to encourage and promote marriage would be to open it up to same-sex couples, but at the same time eliminate all domestic partner/civil union sorts of arrangements. Let it be known that the only tolerated unions for both same- and opposite-sex couples are legal marriages til death do you part, period.