A friend of mine once said that having children was the most selfish thing anyone could ever do because you're forcing your choice to have a child on some poor unsuspecting sprog who has no say in who its parents are. He's since gone on to produce two.
You never know who's going to be a good or bad parent until it's to late. I've seen some people who, on paper, should be disastrous parents doing a great job of it and raising healthy, well-behaved, happy kids in a loving, caring home. Some, who should have been wonderful parents have raised little monsters - maybe that's getting into the nature/nurture thing - and others have turned into complete tyrants and won't let their offspring say or do anything 'kid-like' such as have fun.
Whatever happens, don't decide to have kids or not have kids because of what someone else wants. If you're being responsible about it, it's something for you and your partner to decide (barring accidents), not your parents. Are they going to raise the kid? And going by what you say, you wouldn't want to let them even if they would! Sorry if I sound flippant, but it's either that or I give a sermon. It sometimes isn't your choice whether or not you have children. Accidents happen. Say one night a condom split and a couple of years later, you found out you had a child. Would you walk away? It certainly sounds like you've thought a lot about it, and, more importantly, it sounds as if you've thought about it from the point of view of the child's welfare, not your own. You never know, you might surprise yourself and turn out to be a great dad given half a chance.
Ideally, I'd like to have kids myself some day, but I can't see that happening somehow. Maybe it's the gay thing. My sister has kids anyway, so I'm off the hook from the genetics point of view and it's great to turn up now and again and spoil them and have fun, but the real plus point is to be able to say, "He needs changing," and walk away. Actually, aside from anything else, I don't feel grown-up enough to be a parent. I'm way too selfish and immature.