Big John Dewey in his The Quest for Certainty was critical of philosophy and of certain philosophers for pursuing certainty as a goal. I think he may have underestimated the extent to which certainty is cause for dismay.
We're never more dangerous than when we are certain, particularly when we are certain something is true or good. Our certainty empowers us, renders us self-righteous, impatient of questions, even merciless. Extremism in the pursuit of the truth or the good appears somehow appropriate to us. Means, however dubious, are justified by the much desired, unchallengeable ends.
The 20th Century is seen by many to be characterized by mere relativism, but it seems to me to be one in which certainty was the cause of vast and unspeakable horrors. The Nazis and Soviets, spurred on by Hitler and Stalin, were certain of the need for the acts they took in pursuit of the goals they were certain must be sought. Millions died as a result, Jews, kulaks, Ukrainians, Roma.
I've recently read a book called Bloodlands, which is a detailed description of seemingly endless atrocities and massacres engaged in by the Germans and the Soviets, particularly after the commencement of the Second World War, but before and after it by Stalin in his cruel quest to industrialize the Soviet Union. Page after page reciting deaths by shooting, gassing, starvation, ceaseless labor. It was a numbing experience, but one I feel I must recommend, if only because it illustrates the evil of certainty.
We've been warlike and cruel throughout our history, but it seems to me that our wars for power, glory, empire, money are small things compared with the wars we've waged for religious reasons, or to fulfill our destiny, or bring about the workers paradise, secure in the knowledge that all we do is for truth and the good. The certainty that God wills it, or history or race or destiny require it, gives us carte blanche to do what must be done, whatever it may be.
Napoleon, Alexander, Caesar did a good deal of damage, as did England's wars of empire, but their quests for power, profit and personal glory are mere drops in the bucket of blood filled by such as Hitler, Stalin and Mao. The Roman Empire was a military dictatorship, sometimes viscious and savage, but it required the triumph of Christianity, exclusive and certain, and its usurpation of the empire to render it intolerant not only of rebellion and disorder but of thought and religious belief.
When we believe the state is the means by which we may bring about the moral perfection of its citizens, or the human race at large, we are inclined to do most anything through the state, or to forgive most anything done by the state (this is a lesson Plato's totalitarian republic should have taught us--better Sparta than Athens, according to Plato). There is therefore wisdom behind the view that the state should have limited power, as those on the Left and the Right are equally certain when it comes to what they feel is true or good, and are equally inclined to exercise power in their pursuit when they obtain power. Stupid and selfish as we are, we may do less damage to ourselves than would a government convinced it must do what is necessary, regardless of our wishes, for our own good.
We're still on the quest for certainty, unfortunately. We should teach ourselves to accept uncertainty, to feel comfortable with probability, respectful of the chance for error. It will make us humble, cautious; even wise. Not the most romantic or glorious point of view, but one which may allow us to live in peace. At least it may lessen the chance for mass murder. After the certain horrors of the 20th Century, that's no small thing.