Of course, societal attitudes can become more conservative as well as more liberal. You seem to be assuming that the overall direction is towards greater liberality, but it’s not obvious to me that that’s the case (e.g. the Arab world going from the center of learning during the Islamic Golden Age to the fundamentalist states that many of them are today, various claims that I’ve heard about different fundamentalist and conservative movements only getting really powerful as a backlash to the liberal atmosphere of the sixties, some of my friends’ observations about today’s children’s programming having more conservative gender roles than the equivalent programs in the seventies-eighties IIRC, the rise of nationalistic and racist movements in many European countries during the last decade or two, etc.). My null hypothesis would be that liberal and conservative periods go back and forth, with only a weak trend towards liberality which may yet reverse.
Of course, societal attitudes can become more conservative as well as more liberal. You seem to be assuming that the overall direction is towards greater liberality, but it’s not obvious to me that that’s the case (e.g. the Arab world going from the center of learning during the Islamic Golden Age to the fundamentalist states that many of them are today, various claims that I’ve heard about different fundamentalist and conservative movements only getting really powerful as a backlash to the liberal atmosphere of the sixties, some of my friends’ observations about today’s children’s programming having more conservative gender roles than the equivalent programs in the seventies-eighties IIRC, the rise of nationalistic and racist movements in many European countries during the last decade or two, etc.). My null hypothesis would be that liberal and conservative periods go back and forth, with only a weak trend towards liberality which may yet reverse.