Indeed, for many people on both sides it was (and is!) quite a shocking revelation that in their surroundings there is a huge number of people who don't just disagree on opinions or facts but have completely contradictory values, one side praising that which the other deems as clearly, obviously evil, and vice versa.

I'd argue that this comes from a change in media - where previously you had a clear consensus either in the small community you lived in earlier times, or country-wide with the advent of mass media, and even if you'd disagree with that, then you still can't avoid knowing what the surrounding reality was; but now with personalized social media, so many people get a false impression of the actual social consensus around them, because they communicate much less with people around them but rather communicate in an "information community" which is larger geographically (often global), and which is different from the actual community where they live and which makes laws for their life; so they perceive that the "community standards" go one way (in the way which their "online information community" thinks) but then reality crashes in with something totally different, and this does "break people's minds" in some way.