Yes good on you SD. I would like to adopt, but I suppose it will depend on whoever my future partner is (if I end up having one lol).
Anyway, supposing I do lucky in such a way, I would hope also to have a biological child or children with her. And now, behold my reasoning (in no order):
1) Biology - if I don't raise kids that can have their own kids, I am evolutionarily dead. All the ancestors that worked their asses off to bring me into the world would be silenced, as would my own special genetic combination.
2) Tradition - my brother is gay, and thus will probably not have biological kids. I am thus the only chance my parents have of having biological grandchildren. This is related to the above, but goes beyond - I am also male, and the only person within several degrees of separation that might give our family another generation. I say might because I am not dumb enough to assume I will have a boy, and not chauvinist enough to insist on repeated tries until I have a boy. It matters to me, but nowhere near that much. From another perspective, I feel that whatever sex I was, I would want a child of the same sex, because I know what it's like to be a boy, not a girl. But this is a minor issue. If I could just pick, I would choose male, but I have no intention on forcing that issue at all. Because I know if I were a woman I would want a girl, so it's only fair. One more thing on tradition - people have kids, traditionally. It would be continuing the tradition in that sense as well. This point however is not very important to me. A lot of things about my life are non-traditional.
3) Personal belief - I believe that, contrary to TWA's opinion, life should be created, on principle. Thus if I had the resources to raise I could, my beliefs are such that I feel I *should* do such. As jmo said, I am glad I was born. For the same reason I oppose suicide, I am in favor of birth. Life is a good thing, despite its hardships. Those hardships are an essential part of the human experience, and I would absolutely cherish the opportunity to bring another human into the world and take care of their needs as a young'un.
4) Instinct - This is different from the first reason, which is cerebral. This one is just the "awwww kids!" feeling in me. I see people with kids. I think the kids are cute and wonderful and feel an urge to take care of them. And to have my own. Some people say this instinct is only in women, or is stronger in women. Hell no. I definitely want kids at a primal level, at an emotional level, a logical level. It goes on and on.
Also it would just be so great to get to raise my own kids and teach them what I know. If you don't have kids you never have a captive audience like that. I want to be someone's dad, it's about as simple as that.
That said I know that given my choices I may never have kids. That's ok. Bummer, but I'm not going to have too many issues over it. Or, I hope I don't. Also I might end up being infertile or something, who knows till you try, right? Or she would be.
It would definitely not be a dealbreaker if my partner was infertile - that's fucking terrible. If she didn't want kids at all though.... I would have to think long and hard. That would be a hard choice.