Pornographic Giffen goods?
Well, not exactly, but the logic remains interesting:
At least one major voice in the porn world thinks a small tax — well below 25 percent — might actually have the unanticipated effect of helping the adult industry.
"As soon as we get a universal or national porn tax, we get what we’ve always wanted — that comfort zone of respectability that cigarettes, alcohol and gambling have," said Bill Margold, a former porn performer who now advocates for adult performers.
Margold suspects the "greedy" adult industry will oppose any kind of tax, even if it’s in the 1- or 2-percent range. But "in the long run, they’ll see it’s the best thing that ever happened to them. It is respectability, and respectability has a price tag."
Consistent with this argument, the religious right opposes the idea of taxing porn; here is the story. Addendum: Ben Wieland directs my attention to this earlier post on taxing brothels.