What happens when man's reason is used as a weapon to slice through the accumulated detritus of ignorant and benighted ages and into the glorious new world of Enlightenment?

What happens when man's reason is used as a weapon to slice through the accumulated detritus of ignorant and benighted ages and into the glorious new world of Enlightenment? The old is cleared away and the space is created for the new, but at what cost? Does reason itself have sufficient capacity to create a comprehensive world for man to exist as man, or does he become something else?