I agree with a lot of what you've said in this post, very insightful. I've never had biological children of my own for similar reasons, and it has been the end of a few relationships in my life. As a stepdad, I have the best of both worlds, always trying to do my best while not responsible for bringing them into this world.
Of course I'm being a bit satirical, but not completely.
There is truth to that, though. After all, once someone is in this world already, we may as well choose to share it with them, especially if they are little and need care. Adoption is something I was going to mention, but I was already spreading myself thin in this long post. My wife and I like to joke that we've adopted each other, which makes me her adoptive husband. :-) And adopting children (though I'm pretty certain we're not going to) can have a direct help on those suffering children mentioned in the question. So it is really the best of all worlds, especially since I believe the bond between parents and children is much more psycho-social than genetic.