Many people seem to be arguing abut the effects on happiness. I'm not too concerned about that to be honest. The negative effect on happiness doesn't seem radical and child outcomes aren't that much effected by parental upbringing beyond a minimum once one disentangles the data from genetics so I'm not to worried about responsibility, especially since I think that by the early 20s he is as much a independent agent as anyone today and I don't feel (yes horrible word) like someone else is responsible for my actions. Financial independence is another issue, however again genetics will play a large role in reducing my child's risk for some kinds of poor decisions so really my decisions should mostly be based on my genes.
Not everything that I do pursuing my values will make me happy, especially if some of my values can't really be lived up to by humans.
So I found this post quite interesting:
http://www.gnxp.com/blog/2009/03/gnxp-readers-do-not-breed.php
(I'm quite sure that the demographics of this site closely parallel the demographics on Gene Expression).
Research seems to indicate that people are happiest when they're married, but that each child imposes a net decrease in happiness (parents in fact, enjoy a boost in happiness once their children leave the house). It's possible, of course, that adult children may be pleasurable to interact with, but it seems that in many cases, the parents want to interact with the children more than the children want to interact with the parent (although daughters generally seem more interactive with their parents).
So how do you think being child-free relates to rationality/happiness? Of course, Bryan Caplan (who is pro-natalist) cites research (from Judith Rich Harris) saying that parents really have less influence over their children than they think they have (so it's a good idea for parents to spend less effort in trying to "mold" their children, since their efforts will inevitably result in much frustration). And in fact, if parents did this, it's possible that they may beat the average.
(This doesn't convince me in my specific case, however, and I'm still committed to not having children).