To take the international example: Donald Trump's statements are routinely lambasted as stupid and ignorant. He is seen as the prince of idiocy and obliviousness. But local examples abound, too – look at recent asylum-seeker or marriage-equality debates.

Trump is indeed unable to pursue basic arguments and is demonstrably lacking in crucial knowledge about his own brief. The New Yorker quoted one conservative adviser: "He seems as clueless today as he was on January 20." Closer to home, many leaders' arguments are often absurdly bad. Witness Minister for Home Affairs Peter Dutton's description of pro bono representation of asylum seekers as "un-Australian", or independent MP Bob Katter's bizarre discussion of crocodile deaths.

The problem with these accusations of weak rationality is not that they're inaccurate. The problem is what we might call "the fallacy of inherent intellectual goodness": the belief that enhanced cognition translates into improved morality.

Put this way, perhaps it seems silly: a boffin's conceit. But it is actually a common idea. In civilised debate and frothing rancour alike is the assumption that what really sets one apart from one's opponents is intelligence and knowledge. The logic is this: "If only they were as smart and informed as I am, they'd be good (like I am)."

To begin, thinking is a diverse activity, and has no necessary relationship with ethics and politics. It is possible to reflect rigorously, systematically and with devotion to the facts – and never even sniff an argument about how we ought to live.

Take arguments about aesthetics. Marcel Duchamp's artwork Fountain (actually a signed urinal) invites sustained intellectual effort. For good or ill, it ushered in a new era of art practice, and raised interesting questions about art and the art world. But such discussions, however enthralling to philosophers or art historians, can carry on without once gesturing at matters of morality or the state.

Thought has many ends, and only some are concerned with good or right. In fact, it can be fun to solve intellectual riddles purely for their own sake; for the challenge of the ideas. (Whether a life devoted to these games is justified is another matter.)

Even within ethics, there is no necessary connection between thinking and acting well. Most obviously, this is because "acting well" is a conflicted notion – and rightly so. Believing that thought leads inexorably to one's own ethical position is absurd. Morality is a situation of perennial strife and, tragically, diametrically opposed positions can be equally reasonable.

The assumption of necessarily moral intelligence is also dodgy because even those with good ideas and relevant knowledge don't always behave accordingly. Put simply, folks can be correct but bad. They might be cowardly: too frightened to follow their conscience. They might be selfish, weak-willed or simply not care. As I noted recently, hypocrisy is ubiquitous, especially among politicians. Someone can wholly share our convictions, and our reasons for them, without acting upon them.

Witness Jean-Paul Sartre, arguably the most well-known philosopher of the second half of the 20th century. The French thinker was an enduring and robust defender of freedom: both as a political principle and as a basic aspect of human existence. More than any other modern public intellectual, Sartre celebrated a fundamental link between consciousness and liberty.

Yet he was manipulative and cruel, using his fame and wealth to keep vulnerable young students beholden to him. Biographer Carole Seymour-Jones wrote of the Sartre-Beauvoir nest as "conditioned to be helpless, its chicks ... a growing financial drain". He could be generous and kind, but was nonetheless exploitative: sexually and psychologically. While famously condemning anti-Semitism, he also profited from the purge of Jewish teachers. While doing little to aid the French resistance, he later set himself up as its inquisitor and, abroad, mouthpiece.

The point is not simply that Sartre was a hypocrite or contradictory. The point is that he was brilliant and, morally speaking, this really didn't matter. He was a man with a powerful intellect, and this did little to guide his conscience when it mattered. The same argument might be made for many great minds: they are smarter than most of us but still bastards.

Importantly, this doesn't mean intellect is irrelevant to living well. Morality requires serious thinking, from our daily obligations to higher questions of ethics itself – its nature and scope. Often we must question ourselves and our situation if we're to do good. But raw cogitative power or masses of facts aren't enough.

The chief problem with Trump's character, like that of many leaders, is not smarts but vice. He is, among other things, greedy, cruel, deceptive – and surrounded by very clever people who use their robust brains to keep him in power.

Damon Young is a philosopher and author. damonyoung.com.au