I don't think the theory that consumption drives production holds true when talking about child pornography because the material can be copied infinitely, it's not a finite resource.
Legal porn seems like a strong counterexample.
Getting random people to pay for content is a pretty hard thing to do, and I’d assume illegal content wouldn’t just be taking credit cards either, so the barrier is way higher. The conversion rate looks to me to be abysmally low, and we’re trying to police the whole internet for that.