Anonymous wrote:The state could not legally compel the couple to use birth control or abort if the birth control failed.

Marriage, as in the issue of gay marriage, is about the legal construct of marriage (ie no one is compelling religion institutions to perform religous marriage ceremonies), and the ability to be recognized as married under the law ato receive all legal protections or burdens (tax penalties) of individuals carrying this definition. The legal aspect of marriage also involves terms where the marriage can be dissolved (divorce). As failure to consumate a marriage is grounds for annullment and failure to have sex is grounds for divorce, the act of sex is assumed to present. Sex between two closely related heterosexuals would or could result in the serious genetic defects. Again, the state could not compel birth control or abortion.

Now arguable, two same sex partners who are closely related could have an argument. However, you would need enough of these individuals to amend the law and this is highly unlikely so I don't think you have anything to worry about when gay marriage passes.

Anonymous wrote:I think that the best genetic outcomes come from diversifying the gene pool. I think that it can complicate families immensely if certain boundaries are crossed. When the relationship ended- the entire family would be divided. Not a good way to acquire wealth over generations. I think much of today's standards of partnerships are based on centuries of trial and error...

Anonymous wrote:Because children should be able to grow up in an environment where there is no threat of having to deal with sexual advances from their grandparents, uncles, cousins, etc.