Saying I am against gay marraige, is like saying I am against aliens.
You mean, you're saying that "gay marriage" is a complete unknown whose characteristics you're unable to imagine, and therefore cannot formulate a response to?
Why would you come to that conclusion? Not only can gay couples marry in almost every civilized country, but even in this country, gay couples are forming households with children in exactly the way that heterosexual couples marry and do.
When two men or two women are married, what do you think changes? Inheritance of property goes the same way, sponsorship of citizenship goes the same way, custodial obligations to children go the same way.
Everything goes the same way except for how many penises and vaginas and breasts show up when you invite them out to couples tennis. And what on Earth does that matter?