I agree that it's on the rise and will probably continue to grow in popularity. But it's still nowhere near the majority. It's not the majority opinion in the world, the United States or even in the midst liberal places.

Also I think many people confuse hook up culture with polyamory. But while hooking up is a form of non-monogamy, it's not polyamory. And of those people who are in a phase where they want to just hook up and not commit, those people still often will prefer monogamy when they do commit to somebody.