I'm of the one-kid mindset as well. I wanted (and got) a boy, but I would've been completely happy with a girl as well. My son only 1 1/2 years old, but I've already had several people ask when we're going to have another. I don't see what the mindset is towards having to have multiple kids (or any if that be your desire). Money and time are tight with one, and I'd rather give one a better life than several a life with less time spent with their parents and more time spent at the poverty level.
I had both good and bad experiences with my siblings and don't think my life would've been better or worse without them, just different. My parents' lives OTOH might've been much better without 4 kids stretched across 16 years .
I've read studies about a couple's happiness increasing with the first child but decreasing with every additional child. I've seen that play out in real life as well. People have the make the assumption that one child brings so much joy, so 4 children must bring 4 times that much joy, but I just don't see it.