The first time I can remember coming across the idea was when, nearly 20 years ago now, I read the late Christopher Hitchens’s Letters to a Young Contrarian and was surprised by the author’s contempt for one of my own intellectual heroes, Blaise Pascal, for having proposed his famous "wager" in favor of belief in God. Hitchens seems to have thought that if you believed only because you thought you had something to gain and nothing to lose by believing, which was the essence of Pascal’s Wager, God Himself — if there were a God — would spurn you from Him for a belief based only on a base calculation of its advantages to yourself.
Not only do I doubt that anyone before the 20th century believed such a thing, I doubt that anyone before the 20th century could have believed such a thing. But along with modernism and moral licentiousness there came something of a cultural obsession with purity of motive — perhaps as the twin of that other modern obsession with sniffing out and condemning relatively harmless little social hypocrisies, formerly only (and famously) the tribute that vice paid to virtue. T.S. Eliot gave voice to the new attitude in Murder in the Cathedral:
The last act is the greatest treason:
To do the right deed for the wrong reason.
Like most seemingly "wise sayings" (as they used to be called) this must have been passed on the nod by many a ratifying conscience that never paused to think about what, exactly, was treasonable, for goodness sake, about doing the right thing for the wrong reason? I could see how it might be a form of treason to do a wrong deed (as the world saw it) for the right reason. A lot of the sympathizers with Kim Philby and the Cambridge Five who spied for the Soviet Union no doubt thought precisely that of them. But then they also presumably thought that treason was no big deal if your reason was in the right place. The right deed for the wrong reason, by contrast, might well describe all those who didn’t commit treason only through fear of being caught and executed. How paradoxical, then, to describe them as guilty of treason anyway!
Or, to return to Hitchens’s example, would people who believed in the Christian message on account of Jesus’s threat of hellfire against the unbelievers also be guilty of doing the right thing for the wrong reason — a reason that would make Jesus himself treat you like the Scribes and the Pharisees, or perhaps the money-changers in the temple? But if so, what do they suppose was the point of Jesus’s mention of the threat of hellfire in the first place? It was much more probable to suppose that such an idea could only have occurred to someone like Hitchens who had made up his mind in advance that belief could not be "the right deed" in any circumstances or with any reason. All reasons were wrong reasons to him.
But nowadays the right-deed-wrong-reason topos appears to be taken for granted as no more nor less than a truism — even to the extent that a judicial assumption of impure motivation is enough to invalidate claims of innocence of wrong-doing before the law. That’s what has just happened in Britain with that country’s Supreme Court’s ruling that the Prime Minister, Boris Johnson, unlawfully prorogued Parliament. No one doubted that it was his prerogative as prime minister to advise the Queen to prorogue, which she duly did, but while no one was looking the Court seems to have added an additional test of legality that wasn’t there before. In order for a politician’s act to be legal now it must not only be in accordance with law and custom, it must be done with a proper, i.e. a non-political, motivation.
When, we might ask their lordships, do politicians (not to mention judges) ever do anything for non-political reasons? The only thing preventing such reasoning — which has lately been applied in the American courts as well, against the Trump travel restrictions and the citizenship question on the census among other matters — from paralyzing the political process completely is that the new purity test is most unlikely ever to be applied to any political act that the judges themselves agree with. What, then, shall we say about the purity of their motives? And who is there left to listen to us when we say it — now that the judiciary in both countries has become so politicized?