An approach I've wondered about: what if we were to take only existing CP (previously seized by the government, let's say), for which the model is known, now of age, and consents to this (because they believe it's going to lead to fewer children being abused), and publish it as widely as possible. Continue to bring the full force of the law upon anyone producing new material. Obviously this wouldn't eliminate production entirely, but it seems like it should lower demand a great deal (because what difference does it make to the "user" if a picture was taken fifteen years ago) and at least make it impossible to produce CP for material profit.

My instinct is that this is, objectively speaking, morally good, but would still be unacceptable to the population at large.