The "Overton window" is the name for the idea that there is an acceptable range of ideas in public discourse.
Since the mid-eighteenth century, there has been a trend for the "Overton window" to move "leftward". Many ideas that used to be conservative, conventional wisdom are now "unacceptable" for political figures to express. Many ideas that used to be radical challenges to the accepted order are now part of the accepted order. Some ideas have moved from being radically left-wing to standard to radically right-wing.
Is it possible for the Overton window to split? Are there historical examples of a society with a single range of acceptable ideas becoming a society where there is a range of "leftist" ideas (that are acceptable to leftists), and a range of "rightist" ideas (that are acceptable to rightists), but in-between ideas are unacceptable in political discourse?
Please feel free to provide examples that use faction names that do not fall on a "left-right" spectrum.