Because of the reasons already stated in post 90. I realize that it represents a devastating argument to gay enablers such as yourself, but you can't simply ignore it in a debate. *shrug*
Post #90:
"Bearing children is certainly an important component in the basic building block of society, but not the only one, or perhaps even the most important. It's a difficult thing for liberal men to understand due their feminization, and difficult for liberal women due to their twisted view of equality.
Man's basic instinct is to be a hunter; a predator, to sow his seed widely and command vast territories, regardless of who may make claim to them. Woman's basic instinct is to be a gatherer, a nurturer, to consolidate her holdings and seek cooperation among her neighbors. Separated, the sexes develop disastrous societies, if they develop at all."
I have already addressed these points and they are not valid reasons for not allowing gay marriages.
Your generalizations of gender roles is outdated and obsolete. These roles can be reversed without any harm to society. And both roles can also be held by a single gender in a committed and monogamous relationship.
And your stereotyping the roles and claiming it is a reason not to allow gay marriage ignores the fact that the gay men & women who would marry are already living as couples and society has not been effected.
The simple truth is that these couples already hold the roles you discussed. The only difference is whether or not they can marry. The fact that they are already in these roles and society has not been harmed shows your argument to be invalid.