Our culture hates children. It sees them as an inconvenience. I know that people think they have a lot of good reasons to justify avoiding pregnancy, but their reaction to my wife and me (and other families like ours) belies the more noble excuses people make (i.e. I want to be a good steward of my resources). At least, in my experience. Let me give an example.
By far the most common (somewhere in the 80% range) response I get when I tell acquaintances we are expecting another child is "Do you know what causes that?" As I try to be polite even in the face of such rudeness, my usual rejoinder is something along the lines of "yeah, we've pretty well got it figured out."
Why do I call it rude? Well, for starters, inherent in the question is the belief that my wife is pregnant because we are ignorant. The thought behind it goes something like, "If you really knew what caused you to be cursed with a pregnancy, you wouldn't let it happen."
Along the same lines, the response assumes we don't want more children. Why is that? What is so strange about wanting to have children? Well, in my opinion, it is because having children is truly inconvenient. It's not easy and there are many costs involved -- and I'm not just talking about financial costs. We lack for nothing we need. We have no problem making ends meet and are able to do so on a single income while giving away a sizeable chunk (about 5 times the national average, according to the software I use to do my taxes) and saving a good amount as well.
We don't, however, enjoy all of the material comforts many of my peers do. We don't have a third vehicle. We don't have a big screen plasma TV. We don't have a timeshare, or go on cruises, or vacation in Europe. We manage to enjoy life just fine without any of those things. And we'd rather be blessed with children than any of those other things.
We also don't have time to ourselves. I don't play Ultimate frisbee anymore, or even very much disc golf (usually only on vacations). I don't go hang out in bars or engage in other extracurricular activities. I rarely have time to play computer games, or even read for pleasure (though I do read quite a bit considering our situation). Jamie isn't in any clubs, but I do try to get her out with her girlfriends once a month or so.
My point is, I don't believe (most) people when they make arguments as to why they don't want more kids. I think most people look at a life like ours and say it's not worth it. Having children is too much hassle and too much work and too, well, personally inconvenient.
I'm not saying any of this to glorify the choices we've made and the lifestyle we lead, or to paint myself as holier-than-anyone (God knows I'm not that). I do get tired of the rude responses we get and I feel much more free to vent in this space as opposed to unloading on the next idiot in meatspace who asks me if I know why my wife is pregnant. So take this for what it is, and nothing more. And of course, feel free to take offense and tell me why I'm wrong. 'Tis the beauty of the medium.