I think you ask a fair question and I commend you for giving it so much thought as opposed to others in this world that just have a kid or 5 and see what happens.
I don't have any kids, but I think the answer to your question is people want kids for reasons that don't have a tangible answer. One example would be, imagine looking your very own son/daughter in their eyes and knowing this is your seed, you made this human being...
...and then they start shitting. A lot.
