This is a really good question for discussion in groups of three or four, if you're teaching a class. In fact one of my teachers did just that: he drew a long horizontal line on the board with right at the end of line on the right and left at the end of the line on the left. (You could substitute fascist communist or whatever you like.) Then he wrote some names on the board, beginning with obvious ones like Mao, Hitler, and so on. We, in our groups, had to place names on the left-right axis. Yes, I now know that it's not a continuum and I'm sure he did too and that was one point of the lesson. When you get to the extreme left and right, the weakness of the continuum becomes clear because there is crossover. You could add another dimension like plotting an x y graph in mathematics. Where would Henry Kissinger go?