You quote this as a maxim but it's simply not true. Friends of mine once posted on craigslist: "Wanted: girls to give a yeti a blowjob on camera. There will be pizza." Three chicks showed up. On the other hand, a server at a nice restaurant can make a thousand a night. Exactly. If there were less stigma, there would be less money. That's why there's such a glut of amateur porn nowadays- the high end has gone away because acceptance has gone up. Prostitution is service. Pornography is performance. Prostitution is individualized attention. Pornography is generalized exhibition. There is no comparison.The moral hazard, as it were, may make you earn more than you might otherwise, but take that out and you're still doing better per hour than a waitress.
I can't get past supply filling a demand here.
With prostitution, I would again go back to demand causing a supply.