- It assumes that we are completely in control of our fertility. If we were planning to get two dogs that were four years apart (smart dogs, if we're using the college reasoning!), then we could easily just get two dogs with that spacing. Getting pregnant doesn't work that way. (In case you're wondering, no, we're not trying right now. That's not where this frustration is coming from!) I've read different studies about fertility. One said a woman only has a 20% chance of getting pregnant each cycle, and another said 85% of couples get pregnant within one year of trying. That means 15% of couples are still not pregnant after a full year. Doesn't sound like science supports our controlled spacing, does it? Most importantly, in several places in God's Word, we see him open the wombs of women (for example, see the stories of Rachel and Leah in Genesis 29 and 30). God is in control of whether or not we get pregnant, not us.
- It assumes that we are complete dolts at budgeting. Here's a tidbit of info that I guess escapes those pushing the four year spacing: Kids don't come out ready to start college! Jocelyn was born in 2007; we aren't going to be shocked in 2025 when Jocelyn starts college. I suppose, given the latest stats about debt, it shouldn't surprise me that it wouldn't occur to people that you could save in advance rather than just paying as you go. But we have a budget, and we save. If Calico/Zoe/Arabella or Gavin (our latest names for a girl or boy) comes before Jocelyn is four, then we'll budget to plan for having two in college at one time.
If you want to aim for four-year spacing between your kids, go for it! But don't tell me what my family should do, and don't laud four-year spacing as the only logical, wise, or prudent spacing.