Okay, first up:
Your old testament is "high on big families", because it was written in a time when infant and adult mortality were both very high; it was a societal necessity.
I mean, sure, if your family is so nuts they refuse medical services - fuck away. You're gonna need a big family to make sure enough survive to support you in your old age.
(there are also additional cultural differences that account for a "pro big family" stance - I note that none of these crazy God-fearin' people are discussing the evils of eating shellfish or pork, but the old testament was reasonably specific on that count too)
Secondly:
I've had a few discussions with people lately worried about the "Idiocracy Effect".
While stories such as these may be an initial cause for worry, their claims that
...don't quite hold true.'If everyone starts having eight children or 12 children, imagine in three generations what we'll be able to do,' " Joyce says. " 'We'll be able to take over both halls of Congress, we'll be able to reclaim sinful cities like San Francisco for the faithful, and we'll be able to wage very effective massive boycotts against companies that are going against God's will.'
For starters, if they're struggling just to provide for their families, they don't have the economic resources to make their "zerg rush" effective.
And while it's conceivable that they might sabotage modern education, I'd be surprised if that were successful beyond drinking age, even in the Bible Belt.
Bonus Question:
Demonstrate why, in spite of a trend for wealthier people to not have children, babies are not in fact, an inferior good (despite the fact I like to go around saying it, just to piss people off).