There are plenty of types of relationships that are consensual, but that are still either illegal or else forbidden by the ethics standards for various industries. Just because something is widely accepted today, doesn't mean that it will be acceptable in the future as long as there is consent.
Ethical standards are shaped by the conflict between the world as it exists currently and the type of society we'd like to have. They're not immutable, nor are they guaranteed to move in any particular direction. E.g. if the human population outstrips the supply of cheap natural resources, liberal western values may go out the window very quickly around the world, just like they did in Iran.
History has also been going the opposite direction of what you're claiming anyway. Promiscuous consensual sexual behavior was much more heavily penalized in the past than in the present. It's going the other way. Many people were calling for rock music to be banned back in the day because of this kind of behavior they said that it idolized. Now, if anything, it's celebrated.