Jeremy Corbyn's supporters are making much of Owen Smith's work as a corporate lobbyist for Big Pharma before he entered politics. Whether he behaved unethically is irrelevant. To anyone who knows the culture of the left, his old job description alone can be enough to damn him.

Reciting 'corporate lobbyist' in many left-wing quarters produces the same effect as reciting Satan's name in a nunnery. No wickedness is unimaginable once such a demon is conjured from the depths. As I would expect, Corbyn supporters are already implying on the basis of no evidence whatsoever that Smith wants to privatise the NHS. Whether Smith responds in kind will tell you whether moral arguments can still move left-wing minds.

I can make a fair case for saying that Jeremy Corbyn is the most hypocritical and unscrupulous leader in Labour's history. His paid employment while he was an MP was nothing so elevated as corporate lobbying. It consisted of working for the propaganda stations of Russia and Iran. If you watch the YouTube videos of Corbyn in action, you cannot pretend that he is challenging his paymasters or even politely expressing an alternative point of view. He is a mouthpiece for his ugly employers. A willing rather than a merely mercenary mouthpiece, I grant you. Hatred of the West and the willingness to excuse any state as long as it is anti-Western animated him. He is a propagandist for the love not the money.

Having said that, as he reinforces his employers' prejudices and avoids discussion of their crimes, every one of the consoling cliches that surround Corbyn and his supporters falls apart.

'Jeremy is a decent man'. Really? No decent person is the flunkey of fantastically corrupt states. 'Jeremy is left-wing.' Is he? He has a funny way of showing it. Iran and Russia are self-proclaimed conservative states. Iran is the bastion of theocratic Shia conservatism. It persecutes ethnic and religious minorities - until Assad began his mass murders, Iran was the worst place in the world to be a Sunni Muslim - and jails trade unionists. Putin, meanwhile, tells the European far right to reject liberalism, and embrace his reactionary nationalism. From a Russian point of view, Corbyn and Seumas Milne's most prominent comrade is Marine le Pen.

You cannot support oppression abroad and freedom at home. No one has the right to be shocked by Corbyn's association with a holocaust denier, or his supporters' willingness to resort to the grossest abuse of women, while their Pilate of a leader washes his hands and looks the other way. It is all of a piece.

Yet the moral argument against Corbyn has found few takers. Until very recently, mainstream liberals have been as uncomfortable as Labour members and trade unionists in facing the darkness on the left. It remains a staple assumption of the arts, broadcasting, and comedy that racism and anti-Semitism, say, or hatred of gays, can only be found on the right.

They have erected elaborate defences against the notion that their friends are just as likely to resort to bigotry and stupidity, and are if anything more likely than conservatives are to turn their backs on the victims of oppression in Iran or any other anti-Western state.

If Owen Smith were to campaign on the issue he would be met with an explosion of whataboutery. What about Saudi Arabia, for instance? And indeed it is the case that British politicians support Saudi Arabia's theocratic monarchy and try to pretend there are meaningful differences between its Wahhabi ideology and the ideology of Islamic State. But Western leaders appease because they believe jobs will be lost and oil supplies will be endangered if they break with the kingdom. They go along with Saudi Arabia because they believe they have to. The far left goes along with Iran and Russia because it wants to. It will ally with them and any other anti-Western regime or movement, however conservative it may be. Even their opposition to pro-Western dictatorships is in bad faith. If the Saudi monarchy were to break with Washington tomorrow, they would drop their supposed concern for its victims, as smartly as they dropped their concern for the Iraqi dictatorship's victims, when Saddam went from being the West's ally to the West's enemy.

Smith ought to fight the smears Corbyn is directing against him with inconvenient facts of his own. I wonder if he will dare. His message to date to party members is that Jeremy is a decent guy. I admire him for returning Labour to its radical roots, Smith says. The only thing that is wrong with him is that he is a hopeless politician. If you make me your leader, you can have a competent version of Corbynite radicalism.

In other words, he is trying to flatter them away from their leader. He may fear that if he tells them that their hero is an unprincipled hypocrite, it will reflect badly on them. Either they are fools for not seeing Corbyn's wickedness when they voted for him. Or they are unprincipled hypocrites themselves for seeing and not caring. An attack on their leader's immorality will also be an attack on them. An honest critique of Corbyn would puncture their own self-righteousness. And given the catastrophic position the English left finds itself in, their self-righteousness is all they possess.

And yet, and yet, you cannot talk of left-wingers as a bloc. Many who joined the Corbyn movement have had a hard political education, and been repelled by the foul air of intimidation it has brought into Labour politics. Owen Smith may hope that an honest critique of Corbyn will shift more away from him. Most Corbyn supporters do not, he may calculate, believe in excusing and indulging Russia, Iran, Hezbollah and Hamas. They are decent people at heart motivated by justifiable fury at the rotten state of England.

Whether Smith goes with hope or fear will tell us much about him - but much more about the modern Labour Party.