The concept of a strict Left-Right political spectrum is utter garbage given how many different ideologies have come into existence after the creation of the printing press. The Political Compass works slightly better trying to split it by both social control and economic control, because at its core the operation of government is predicated on how much you want to your fellow man to lose his natural rights. (The website itself has its own biases but the concept of a political square makes more sense than a statist-anarchist dichotomy) However, good luck getting the average person to mentally visualize and remind themselves of such a concept when debates get intense or inflammatory. Binary choice is the easiest for humans to interpret and accept under stress (fundamental physics is kind of binary too), so they prefer that over anything else.

Even so, those conflating disagreement with both sides as being pro-leftist or pro-rightist, don't seem to believe in Horseshoe theory either (a theory easily solved by the Political Compass square). They could be authoritarians in their own bullshit, just have deluded themselves into believing they're not. Some of the way users talk here about is the same as the way I've seen extreme leftists talk "centrist/third part position is letting the right-wing Nazis win"

Add: Another issue is that society has drifted so far that we're stuck debating issues that used to be fundamentally agreed upon with natural conclusions. Issues where you should have significantly different opinions are ancillary. The problem is that ancillary issues are conflated with fundamental issues, so it's far more likely you'll get flagged as being the enemy when discussing ancillary ones.