As far as the Prohibition reference, it is very relevant to the discussion. People who want porn will be able to get it regardless of laws. The only thing is, they would be getting it from the same people who currently supply pot and cocaine, and the porn they get will be FAR more hard-core.
It doesn't matter what laws we have on porn production when people can download hours of it from an encrypted connection to an overseas server, and when hours of porn video will fit on a tiny flash card. Any laws you try to enforce will be counter-productive.
The military has a maxim: "Never issue an order which you know will not be obeyed". The corresponding maxim for politics is "Never create a law which will be openly flouted by a large percentage of the population", because doing so produces contempt for the law in general. Moral issues need to be handled by persuasion and social censure.
Which is why I view the nationwide 55-mph speed limit law as, quite possibly, the most destructive law that we ever had. For it was flouted by every driver in America at one point or another. Which then led to a general contempt of law in general.
Same for all speed limit laws. Every driver has violated them at least once.