Well put. IMHO, the vast majority of conservatives--even real ones--miss the most fundamental aspects of the issue:
- The concept of a family union headed by a group containing exactly one male and at least one female predates government, if not humanity itself (animals of many species form pairs that mate for life, and distinguish between attached and unattached females). The role played by such unions is totally unlike the role that is typically associated with any other sort.
- If a man knows that his wife has not had and will not have sexual relations with anyone else after marriage, nor in the nine months prior to it, then the man will know (just as accurately as in the above scenario) that he will be the biological father of all children born into the marriage. Note that husbands need their wives to be monogamous to know the identity of their children, but wives have no such need from their husband. Even if a woman's husband sleeps around, she could still be 100% certain that she'd be the biological mother of any children she bears.
- The ideal environment for raising children is to be cared for by their biological mother and father. Being raised by biological kinfolk confers some benefit, as does having male and female parental role models. Being raised by one's biological mother and father combines these benefits.
- Many people, companies, and institutions voluntarily bestow benefits upon couples whose relationship which fit the commonly-accepted meaning of the term "marriage"; many of those would, given a choice, opt not to provide those benefits to couples or groups whose relationship does not fit such meaning. The real reason for the "gay marriage" fight is that gays want the power to compel other people to recognize their relationship as the equal of marriage, and to demand that anyone who voluntarily bestows benefits upon married couples must involuntarily bestow benefits on them as well.
The last point is perhaps most important, in that it cuts to the real nature of the freedom that's at risk. The issue isn't about what gay people can do in the privacy of their own home, nor even how they can introduce themselves in public. Rather, the issue is what they can force others to do for them.