Just because someone made the decision doesn't mean you should not be disappointed in their actions. If your child started using heroin would you be upset? Of course, that is a bit of a hyperbole, but the point still stands. I would argue that, with some exceptions, the VAST majority of the time, working in porn is a destructive behavior and also often indicative of underlying issues. Very rarely will they become career pornstars, they will be affected negatively socially, it will impede future career growth elsewhere, and may also be emotionally damaged by the experience.
Then, on top of this, there is likely an underlying issue why they are doing porn in the first place. If it's money, I'd hope my child would not turn to selling their body on principal, just like I'd hope they wouldn't rob a store (even when ignoring the victims). There are also likely issues with seeking validation and having limited self-worth, which is why I'd be disappointed in myself.