In actuality, both require you to sell your body, and both can have long standing health effects. If anything, I would say the typical OF model sells their body much less than an athlete. I mean, I don't think they're going to tear their ACL.
And also, both offer no real tangible value to humanity. Sports do not produce anything, neither does porn, they're purely for entertainment. A cashier at McDonalds is providing more absolute value to the world than even the most esteemed athlete.
That's not to say that athletes are bad, entertainment and games are important. But you can't just say one form of mindless entertainment is more valuable than another form.