Most people are followers who simply go with the flow - they do whatever the collective zeitgeist deems good. As you change what's "acceptable" in polite society, you change what's "tolerable", and raise up people once on the fringes to "barely tolerable" status. The shifting of mores should happen naturally over time in various conflicting directions and find some equilibrium within a culture, but leftists are making sure culture only moves in one direction. (or more precisely in various degenerate directions that lead nowhere because all they do is deconstruct)