Precisely so. Let me give you an example: in medieval times it was taken as fact that the king's authority came from God, that god wanted you to obey, and so f

Precisely so. Let me give you an example: in medieval times it was taken as fact that the king's authority came from God, that god wanted you to obey, and so forth. That sounds absurd today, but at the time no other point of view was available. The way to see through that belief is to ask, who does that belief benefit? It was in the material interest of the king to promulgate such a belief system regardless of whether it was true. In the same sense it's now in the material interest of the investor and political class to promulgate the belief that unfettered capitalism is the only rational economic system. But who benefits? This isn't my own original idea mind you. Marx called it "dialectical materialism". Certain scientific facts can be proven. You can measure things like the speed of light for instance. But ideology always reflects the material interest of some group or another.