Gay marriage.

The debate over gay marriage is, at its core, a debate over the purpose of marriage. If you find marriage as a social construct designed to further the breeding process, of course you'll object to gay marriage. And sterile marriage. And marriage involving persons who were exposed to substances that may reasonably lead to birth defects. And post-menopausal marriage. Sure, I'm all for clarifying that "marriage" means "breeding factory." That is, I'm all for stripping my grandparents of their half-century old marriage license.

Of course, if you're all for classifying "marriage" as "love factory," I'm not sure I see what the problem with two guys getting hitched is...