The arguments made by Proposition 8's defenders in the federal court trial fell apart when even their own experts were unable to articulate how, for example, same-sex marriage would in any way harm opposite-sex marriage. Apparently feeling a little low on reasonable explanations for why gay and lesbian couples should be prohibited from marrying, lawyers added a new twist into their argument before the U.S. Supreme Court, and this one might be the strangest yet -- and the most easily attacked.
Rather than sticking with the old argument that marriage exists for procreation and the raising of families -- since same-sex couples do have children and do raise them -- the lawyers argued that same-sex marriage is an institution uniquely designed to make sure that unplanned pregnancies occur within the married state. Good luck with that.
Because same-sex couples don't generally have "accidental" offspring, they wouldn't fit the bill.
Let's quickly skip past the most obvious flaw in this reasoning: It argues that heterosexual couples who clearly would not have unplanned pregnancies because of the couple's age, or infertility, or just really responsible use of contraception, shouldn't be allowed to wed either.
The apparent reasoning behind this argument is that it is better for children and society for childrearing to be carried out by a married couple. And let's assume that's true. In that case, it's true for the children of same-sex couples as well. This is sounding more and more like an argument against Proposition 8.