On the new-books rack at a nearby college library is one titled “Polyamory”. That’s the problem with being a progressive – you need resistance to keep moving forward. Progressives must necessarily have something to push against. Ten years ago they couldn’t gin up much resistance to polyamory. People either dismissed it as ridiculously unlikely, or wanted them to shut up about it for tactical reasons. Now that those tactical reasons are no longer operative, and now that it seems a good deal less unlikely, the progressives can start militating for it.
Maybe the next big cultural battle won’t be over polyamory, but it will be over something currently opposed by most people. It has to be. That’s what puts the “progress” in “progressive.”