No one argues that different economic systems or political systems are one and the same. Capitalism and socialism are so obviously at odds that their differences hardly bear mentioning. The same goes for democracy and monarchy.Prothero restates the same basic point nearly word for word in pieces he wrote to promote his book in the Boston Globe and the Wall Street Journal. And in both cases he leaves this "argument" just as sparse and vague as he does in his book. One really does wish that Prothero had bothered to "mention" a little more of his own thinking on these matters.
After all, as I write this, the Queen of England is pondering whom she will approve as the next Prime Minister of the UK. And whomever she chooses we can all rest assured that the Brits will continue to mix their capitalism with very large doses of socialism, and that their democracy will never dare, as it so far never has, go so far as to try to make do without the bloody monarchy. Indeed, the Conservatives and the Liberal-Democrats in the UK are no more likely to call for the dismantling of the socialistic National Health Service than is the Labour Party to come out in favor of regicide.
Not only the UK, but Sweden, Norway and Denmark all have both democracy and monarchy. And those Scandinavian lands are also the iconic examples of the European Social-Democratic "Welfare State" phenomenon in which capitalism and socialism are inextricably entwined.
So on the face of it, Prothero's analogy falls flat upon consideration of real world examples of capitalism, socialism, democracy and monarchy. The bright lines that Prothero wishes to draw starkly dividing economic systems and political ideologies are easily and often crossed, except, it seems, in Prothero's mind.
But there is a far more significant problem with Prothero's analogizing. For there are cases in politics and economics which do call for the drawing of bright lines, and lines that must not be crossed: in particular when it comes to totalitarianism.
Surely if Prothero had wanted to really drive his point home, he should have talked about absolute monarchy, Communist one-party states, Fascism, military dictatorships, forced collectivization, outright slavery, and so forth. (It must be emphasized that these are all very real economic and political phenomena that the West has had very real, and all too recent, experiences with.) Then he would have been saying something.
But Prothero wasn't willing to go there. It would have required him to tell us which religions we are to compare to Nazism, and which we are not. It also would have required that he have some idea of what he is talking about.
[See also: Contra Prothero, Part One & also The Basis Of Universal Spirituality]