Oh, tell me who was it first announced, who was it first proclaimed, that man only does nasty things because he does not know his own interests; and that if he were enlightened, if his eyes were opened to his real normal interests, man would at once cease to do nasty things, would at once become good and noble because, being enlightened and understanding his real advantage, he would see his own advantage in the good and nothing else?It was Socrates, of course -- he makes that argument in the Protagoras, at the very beginning of the philosophical tradition. It's presented as part of a utilitarian argument -- i.e., that good and evil cash out in terms of pleasure or pain -- that Socrates doesn't seem very wedded to in other dialogues. But his idea that evil is a kind of ignorance is something that appears very regularly in his words as Plato reports them. I won't reproduce the long argument here, but if you want to follow it, scroll to "When men are overcome by eating and drinking and other sensual desires which are pleasant..."
We have firmer reason to think that Socrates held this view, too, because Aristotle also ascribes it to him in the Nicomachean Ethics (scroll to section two of this part, which is Book VII).
Also it is interesting to me that the Guardian author, Pankaj Mishra, seems to regard the rhetorical question as adequately forceful to settle the matter -- at least in the light of, as he cites them, Nietzsche, Max Weber, and Freud. In fact, Socrates has kind of a good argument. Aristotle devoted a substantial part of a book to considering the problem.
We know that people do act in ways that they certainly must know are not in their best interests. The classic case is addiction, but that medicalizes the problem in a way that may make it seem as if the moral philosophy no longer applies. Rather, many who drink as if they were alcoholics prove to have no physical addiction to alcohol. They know, of course, that there is a long term harm that is all but certain if they continue in this manner; the only thing that can save them from it is dying young.
But of course dying young is a possibility, in which case the harm is completely avoided, and whatever pleasures came from the drink were obtained free of charge. So you have a case of an immediate certain gain (at least of pleasure) in return for an uncertain future harm. However, the gain is marginal, and the harm is extreme.
This is one kind of calculation that Nassim Taleb says human beings regularly make badly. So it may be the answer is not that humans are irrational, but that this is a place where human reason regularly leads to a conclusion that is in conflict with itself. The best choice is regularly indicated by reason to be just what a more formal examination of the case would suggest it is not. That is, we very regularly choose the short-term certain gain and dare the uncertain (but quite likely) immense future harm. But our formal examination suggests this is not the wise way to proceed, even though it is how we do in fact reason.
Perhaps it is that we came up in a more dangerous world, one in which the probability of living long enough for those future harms to materialize was not so very high. Socrates, though, was an old man when he died (of execution, not illness). Life spans haven't grown that much in recorded history; it's just that more people died of things like childbirth and childhood. And it would seem that both of those examples would favor an evolutionary response that mitigated against pursuing immediate pleasures in favor of longer-term gains.
So let's not treat this as an easy or settled matter. It's still an interesting question.