I'm not quite sure you can make that leap. While it certainly fits his criterion of a large non-practicing audience, you forget that it actually lacks art (99% of the time). It's as workman-like as accounting or perhaps more akin to a sport.
that would require the audience to consist of people who make porn
No, his argument is that "major art" is widely consumed by people who do not practice it. He uses poetry -- consumed by a small audience of people who almost entirely consider themselves poets -- as an example of "craft." I disagree with his definitions here. They aren't meaningful.
oops, yes, i misread your argument. agreed, porn would definitely be a "major art" by that criterion. (and really, who's to say it isn't? it's an orthogonal classification to good/bad art.)