Porn at the same time reflects and stimulates real life fantasies in basically the same way that any kind of fiction does. The fact that something happens commonplacely in real life doesn't make it any less likely to be included as part of a work of fiction; and doesn't make the work of fiction less likely to be popular.

So I don't think porn would disappear in a sexually openner society.

Although maybe it would change in character, as the taboos of sex reduce and disappear - but that's about what types or fetishes of porn are shot, not about porn in general.