Did our belief in the scientific method (the idea that truth could be gotten at through experimentation) contribute to the notion that we all might have something important to say or to add to conversation? It seems that notion had broader, unscientific, roots. Martin Luther, most notably, was a non-scientific-method advocate for the individual's ability to think for himself. And the idea that each of us can think for ourselves seems, to me, to be the root of individual liberty.
But still the question lingers - why did the pre-eminence of the individual thinker (and actor) rise in the West? Robert Wright made an argument in Nonzero that what set the West on a separate trajectory from the East was the happenstance of power being divided between the church (Rome) and the state (France, Prussia, etc.) - whereas the norm everywhere else was to have the state and church (or whatever spiritual cosmology was practiced) one and the same. I wonder if it was merely this split - and that individuals had to think for themselves to reconcile the differences between the Pope and the King - that sprouted the idea that the individual and his thoughts were to be valued and respected. If the powers that be can't figure things out for us and we have to think for ourselves, by george, let us think for ourselves. Voila, liberte.