I personally wouldn't. In fact, I probably wouldn't adopt a child at all.
Like arkillian, said, some people have pride in their bloodline, and I'm one of those people. I guess that's what happens when you have an old blue-blooded family and get your geneaology hammered into your head from day one.
So it's basically have a bio-kid, or none at all, and the second is looking far, far more likely. XD
It sounds selfish, but you really have to look at it from my very odd, somewhat outdated perspective.
You can only get the clap so many times before it turns into applause.