You're talking about apples and oranges.
Prohibition was the prohibiting of a permitted substance and one which, furthermore, had a long and positive history in human culture. That said, if you know anything about the 19th/early 20th century, it had obviously become a problem in the unrooted US culture of the time, so I can't say that Prohibition was necessarily a bad idea at the time. But it was unworkable, simply because there is nothing wrong with a bit of moderate consumption of alcohol and this has been part of human culture since the dawn of time.
On the other hand, pornography was never acceptable in the US, and has never been completely acceptable anywhere else (which is why even early 20th century French dirty old men had "secret" collections in their dresser drawers when they died!). Beautiful images of beautiful people are one thing; pictures of people doing disgusting things with animals, being tied up and beaten, or torturing children are an entirely different matter.
If the Archbishop gets his wish, everybody in the US and the world is going to have to ask themselves (a) exactly what are they watching and why are they watching it? and (b) is that the kind of person they want to be? Questions that need to be asked, IMHO.
It appears that if the Archbishop gets his wish, everyone in the US and world will have a government bureaucrat asking them (a) exactly what is it you're watching and why are you watching it, and (b) is that the kind of person we want you to be?
In a self-governing nation it is for each of us to decide on the desirability and necessity of these questions. IMHO.
By contrast, porn in America flew relatively under the radar until the 1960s. The only major legislation that dealth with pornography on the national level was the 1930 Tariff Act and that only prevented a person from bringing pornography in from another country(with good reason. German porn is really disturbing). There were various local ordinances limiting and prohibiting the sale of Pornography (sort of like alcohol "dry laws"), but like most other vices, it was considered a personal indiscretion. Even today's standard of "obscenity" as defined by Miller v. California is at best vague.
The average person wouldn't confess to owning or possessing pornography in the same way they wouldn't confess to being an inebriate. While it would be nice if everyone in America was a fine, upstanding, moral person, unfortunately, that's not the America we live in and it never has been. Ultimately, we aren't talking apples and oranges, we're talking simple supply and demand. If you take away the supply, it doesn't get rid of the demand, it only makes the supply scarcer and more valuable. Ultimately, you are not solving the problem of a desire for pornography or people who become psychologically addicted to pornography. Banning pornography just serves to make you feel as if you've actually accomplished something worthwhile.
I'm also glad to see that you didn't actually disagree that if the production or possession of pornography were criminalized, that it would only be a matter of time before it became a new source of income for organized crime.