I think many people are just afraid to try. I’m not all that plus a real-meat cheezburger, so if I can get through my life, I figure lots of other people could, do. It’s not my business if they don’t, of course, unless they’re obnoxious to me, first ;-).
When people say, “I just don’t think I could do it,” I don’t say, “Well, you know yourself best ...”. And when they say, “We couldn’t afford more than two,” I don’t say, “That’s funny, because a house on your block just closed for 2-1/2 times what mine cost.” But sometimes I’m thinking it!
I tend to avoid discussions about it because some people I know are very sensitive about having both parents work full-time when they obviously don’t really need to; the money they spend on cruises, adult toys and the like would more than have allowed for more children. Instead they have strangers raise their children, and are VERY hostile whenever the topic is brought up (even if it is between other people and didn’t involve them in any way).
I must admit a lot of times it isn’t much fun, but I really couldn’t imagine it any other way. If I didn’t intend to have children I certainly wouldn’t have married; then I’d just be dog-sitting for my wife!