Although in truth I personally don't use the bioligical argument when defending my stance against gay marriage, so I'm just nitpicking.
The great majority of those who are strongly opposed to gay marriage are motivated by their religious beliefs.
All the "reasons" and "statistics" they cite are really just a cover to hide the true basis for their opposition. -WackyKat
I've got a statistic. Number of homosexual unions which has produced a child: zero. -NutCrackerBoy
What I meant was to highlight the original reason for government's involvement in marriage: to protect the children that naturally come from the sexual union of one man and one woman.
I personally don't use the bioligical argument when defending my stance against gay marriage. -mcg1969
I don't wish to quibble about artificial semination. A repeated fallacy of the anti-traditional-marriage folks is to cite individual exceptions as if they negate the broad sweep. Men and women procreate, and the state, for the good of civilization, involves itself. Without marriage law, chaos would likely have resulted from men abdicating their responsibilities to their wives and children.
The "biological argument" is a generalization yes, but a profoundly true and important one.
Did you see the custody case in the news last week? One woman gave her eggs, which were carried by the other. Now they're both claiming to be the mother. Oftentimes I long for simplier days.