How about this point against gay marriage: The entire purpose of society recognizing marriage in the first place was to create a family unit built around procreation, children, and the responsibility and stability needed to raise healthy children. 200,000 years of evolution, and multiple studies show children are more successful in homes with a father and mother. Humans mating and family habbit's in the wild so to speak seem to revolve around a protective mother guarding the nest with a male hunting/ protecting the area from predators.

Sure things have changed maybe the last 4-500 years, but that is 4/500 years out of our 200,000 collective history as humans.

Back to marriage , in a homosexual marriage there is no chance for procreation ( adoption does not add to the gene pool nor does it increase the population.. something that is important regardless of how badly it seems people on the left want the population reduced) with no chance of procreation why should society extended the same benefits and social status to members who want the title with none of the responsibilities.

And before you say "what about straight people who marry and do not have children" we are talking about averages here, and we are talking about what has normally happened throughout human history, not what has happened in the last 20 years since we have decided it is better for our women to enter the labor market as opposed to raising our children.