A direction of thinking is not unlike a direction of travel, in that distance often determines context. If you travel West long enough, you will inevitably arrive East of where you began; by an analogous condition, any line of thought will eventually follow the curve of human experience back to where it began, passing through what was originally a polar opposite position. This is why people who decry murder will murder to prevent it, why people who fear revolution will stage a coup to save the state, and why people who seek to protect the moral certainty of their position will invariably stray into immorality in the pursuit of that defense.
It is by this mechanism that idealists become extremists.
