Radically different conclusions about a whole range of issues have been common for centuries. Many have tried to explain these differences by differences in conflicting economic interests. Others, like John Maynard Keynes, have argued that ideas -- even intellectually discredited ideas that political leaders still believe in -- trump economic interests.
My own view is that differences in bedrock assumptions underlying ideas play a major role in determining how people differ in what policies, principles or ideologies they favor.
If you start from a belief that the most knowledgeable person on earth does not have even one percent of the total knowledge on earth, that shoots down social engineering, economic central planning, judicial activism and innumerable other ambitious notions favored by the political left.
If no one has even one percent of the knowledge currently available, not counting the vast amounts of knowledge yet to be discovered, the imposition from the top of the notions favored by elites convinced of their own superior knowledge and virtue is a formula for disaster.
Sometimes it is economic disaster, which central planning turned out to be in so many countries around the world that even most governments run by socialists and communists began freeing up their markets by the end of the 20th century.
That is when the economies of China and India, for example, began having rapidly increasing growth rates.
But economic disasters, important as they are, have not been the worst consequences of people with less than one percent of the world's knowledge superimposing the ideas prevailing in elite circles on those subject to their power -- that is, on the people who together have the other 99 percent of knowledge.
In both cases, the deaths exceeded the deaths caused by Hitler's genocide, which was also a consequence of ignorant presumptions by those with totalitarian power.
Many on the left may protest that they do not believe in the ideas or the political systems that prevailed under Hitler, Stalin or Mao. No doubt that is true.
Yet what the political left, even in democratic countries, share is the notion that knowledgeable and virtuous people like themselves have both a right and a duty to use the power of government to impose their superior knowledge and virtue on others.
They may not impose their presumptions wholesale, like the totalitarians, but retail in innumerable restrictions, ranging from economic and nanny state regulations to "hate speech" laws.
If no one has even one percent of all the knowledge in a society, then it is crucial that the other 99 percent of knowledge -- scattered in tiny and individually unimpressive amounts among the population at large -- be allowed the freedom to be used in working out mutual accommodations among the people themselves.
That is why free markets, judicial restraint, and reliance on decisions and traditions growing out of the experiences of the many -- rather than the groupthink of the elite few -- are so important.
Elites are all too prone to over-estimate the importance of the fact that they average more knowledge per person than the rest of the population -- and under-estimate the fact that their total knowledge is so much less than that of the rest of the population.
They over-estimate what can be known in advance in elite circles and under-estimate what is discovered in the process of mutual accommodations among millions of ordinary people.
Central planning, judicial activism, and the nanny state all presume vastly more knowledge than any elite have ever possessed.
The ignorance of people with Ph.D.s is still ignorance, the prejudices of educated elites are still prejudices, and for those with one percent of a society's knowledge to be dictating to those with the other 99 percent is still an absurdity.