This is VERY difficult to measure. Just 15 years ago, most people thought of porn actresses as something akin to prostitutes. Porn was illegal to make in most of the country (I think florida, California, and nevada were the only places where it was legal) because the law in most states put it in the same category as prostitution.
Prostitution is an industry ripe with lots of "damaged" women, many of whom are runaways with drug problems and a history of sexual abuse.
In Nevada, where prostitution is legal and the state regulates the industry, the stigma is somewhat lessened. So yes, there are still "damaged" prostitutes in Nevada, but there are plenty of women who enter the profession legally and voluntarily without any "damage" per say.
Flash forward to the internet age, and porn is now a huge industry. Women watch porn MUCH more now than they ever have. They enjoy it. Men can now watch porn WITH their girlfriends and wives. It has become akin to a sexual aid like dildos, instead of the marriage wrecking, vice it was once seen as. With that acceptance comes a notoriety for the porn stars. The industry is safer, and the actresses are treated like "talent" instead of fodder. The girls getting into the industry now have grown up masturbating to porn, and enjoy it. They seek out the profession as a career choice. My guess is, very few of the porn stars 10 or 15 years ago did that. They probably "fell into" porn, much the same way prostitutes in states where it isn't legal do.