Actually, I think a circle is too simplistic (though, obviously better than a line). There are a number of vars here:
1) Economic Theory
works with the line
2) Social Theory
still good with a line
3) Stability
now we get complicated
Because I argue the far left is completely different from the far right, but also incredibly unstable. So we have at least two axes: the classic line, but also a line of social order and stability.
Communism in a 'pure' form is incredibly unstable and likely to fall over to strong man politics. This is also true on the far right. The ethos are still completely opposed, but the instability often leads to the same path - autocracy. And in autocracy, political view is totally irrelevant - the individual, which is far more complex than a single ethos, is the entire graph.
But even then, they're not completely opposed at the far extremes, are they? Nationalism leads to suppression of speech. But so does anti-hate speech (for entirely different reasons, and ones I prefer personally, but bear with me - I'm doing thought exercises here).
So in the end it all ends up as a multi-dimensional cube. But the trick is to move gradually and ensure stability with movements. Wild swings in either direction contribute to the native instability of the part of the curve you're on - like jumping to the very edge of a disk spinning on an axes...near the axis is stable, the further away the more likelihood for falling off.
So expect a paint drawing of spaghetti with Hitler, Churchill, Stalin and FDR mixed in.