I think maybe the people who are against gay marriage don't really get what marriage is about. Also the people who think adoptive families aren't "real" families.
Maybe these are the same people who think your wedding is the best day of your life.
A wedding is one day. One. Out of your whole life. And while sex is an important part of marriage, it's really hard to spend a whole day doing it, especially when you've got jobs and kids and a lawn to mow. One of the reasons people like marriage is that when you get busy with raising kids and working and whatever other responsibilities you have, it's hard to spend time finding someone to have sex with. It's convenient to have your sex partner living in your house. (And for those who choose to reproduce, it's also handy to have the other person responsible for that kid's existence around to help with the work of parenting.) But most of your day is spent doing other things, like sleeping and going to work and changing diapers and driving your kid to school and doing laundry.
I believe it's generally better to have two people around and in charge if you're going to raise kids. Not everybody chooses to do it this way. I know some great single moms. But parenting is a job that runs 24 hours, seven days a week, and it helps to have another person around to share the work load. And I have to say, for that job, it doesn't really matter what genitals you have.
It's true that I don't want to marry a woman. But there are lots of men out there I don't want to have sex with, either, and I don't begrudge them spouses, so why would I stop two women (or two men) from marrying each other? It makes no sense.
Same goes for adoption. Giving birth is one day (hopefully less) of your life. Throw in pregnancy and I'll round it up to a year. Which is a significant amount of time, I'll grant you. But my parents have been parenting for forty-three years now, and they don't mention the part where my mom was pregnant very often. As far as my brother is concerned, I'm pretty sure his birthday was the parenting day my mom liked the least out of his whole life. My birth story comes up from time to time because it went a lot better, but mainly my mom talks about the getting me part more than the birth part. Guess what? I have a "getting her" story about Boo, too. And it's much more appropriate to tell at the dinner table.
Then there are people who say they have a special bond with people they're biologically related to. I don't really buy that one, either. I'm close with parts of my family, and not close with other parts. I'm a lot closer to my third cousins on my mom's side of the family than I am to my first cousin on my dad's side. You know why? Because I grew up with my third cousins in my life, but my dad wasn't speaking to his sister for parts of my childhood, so I didn't really grow up with my first cousin.
Which brings me back to marriage. I already knew I could love someone like family whom I wasn't related to before we adopted Boo. Because I had already done it with Hopper.
That's right: adoption and marriage are essentially the same thing. And that's the point. When you decide to make a family with someone, you do it. And then you get to go through life together, hopefully making happy times happier for each other and sharing the burdens during tough times. That's what marriage is, and that's what having kids is, except that in a marriage you try to shoulder the burdens equally, and when you have kids you start out with all the burdens and kind of ease your kid into the burdens she has to carry for herself.
To do that, you have to believe in it. You have to want to do it. That's all. Skills help. Love helps. A good sex life helps. You know what doesn't matter (beyond personal choice)? Gender. Race. Age. Health status. Cognitive ability.
So stay out of other people's choices. There is nothing more personal in this world than how someone chooses to make a family. Whether they choose to be single, to live in a commune, to get married, to have kids--as long as they're not in an abusive situation and they're freely choosing it--it's not anyone else's business.