Who is responsible for defining the legitimacy of an authority?

Anarchism is a broad current. There have always been several movements. But for many, the common point is rationalism. We are rationalists. Like Bakunin, we believe that human freedom is not at the beginning of history as Rousseau could think, but it is at the end of history. By reason, as human beings gradually come to understand the world, to understand their own condition. There is, therefore, a historical progress which manifests itself, and human liberty increases. Therefore, the illegitimate forms of authority, we gradually discover them in History. I give you a concrete example: in the relations between men and women, immense progress has been made in the last fifty years. Where authoritarianism was not perceived half a century ago, it is now found that these were reports containing illegitimate forms of authority and were being tried to combat them.