David Carlin gives us a fine treatise in The Catholic Thing with the central philosophical error of the Enlightenment (and it isn't what I've heard before). He ends with this phrase (click on it to see the full article).
That sums up quite nicely the entire reason for the Protestant Rebellion and the subsequent Dictatorship of Immoral Relativism. The whole intent was to confuse the conscience on right and wrong, and remove the definition of right and wrong from the power of God (Divine inspiration) and put it in the hands of individual men (conscience). It's the Garden of Eden all over again.
Patrick Madrid makes a similar point in a story about an elderly extraordinary minister of the eucharist.