I came here (finally) to point out that the "you will regret not having kids when you are older" sentiment is not without merit and although not everyone will regret not having kids it MIGHT happen and at some point it will be too late.
On the other hand, one of my kids just had 1 hour rage-episode for no obvious reason and she was screaming incoherently and refusing to explain what was troubling her...
Yeah, kids are troublesome and even though our kids have been surprisingly healthy and well behaved in comparison even I and my wife have at one point or another had had enough...
Don't get me wrong, kids are wonderful and I am grateful of having them but I can totally understand why some people don't want to have kids.
Then again, I'm not the kind of person who would go around telling people to have kids. (Unless they come ogling at my babies. At some point the women who fawn over any babies they see become too annoying. GET YOUR OWN DAMN KIDS!)