How can the Labour party have gotten into such a mess that it can be credibly accused of anti-Semitism? An under-appreciated part of the answer, I suspect, lies in the fact it is dangerous for politics to be seen as a moral project.

I mean this in three senses.

One is that some of the left has adopted the cause of Palestinian rights in the way my generation became active in the anti-Apartheid movement - as a moral crusade, a simple matter (in their minds) of right and wrong. Of course, it is trite to say that there's a distinction between anti-Zionism and anti-Semitism, and rationally there is. But an interest in Israel-Palestinian affairs does not often enhance one's rationality. Some of the most passionate pro-Palestinians have blurred the distinction.

Secondly, there's a form of moral self-licensing. If you believe you're the good guy acting for a good cause, you can sub-consciously give yourself a license (pdf) to behave badly: this was one psychological mechanism behind the Oxfam debacle. This, I suspect, has been Corbyn's problem. His belief in Palestinian rights and his active anti-racism has led him to be insufficiently sensitive to some anti-Semitic tropes on the left.

There's something else. That notorious mural contained a big truth - that, in capitalism, some are the oppressed and some are the oppressors. This would be just as true, though, if the oppressors had been depicted as George Clooney lookalikes rather than hook-nosed Shylocks.

The point here is that capitalist oppression is structural. Workers are not exploited because capitalists are bad people. Instead, exploitation is an emergent process - it arises from the nature of capitalism, independently of anybody's intentions. Marx was clear on this. The worker's unhappy condition, he wrote "does not, indeed, depend on the good or ill will of the individual capitalist." Instead, he continued:

Free competition brings out the inherent laws of capitalist production, in the shape of external coercive laws having power over every individual capitalist. (Capital Vol I Ch 10, part 5)

The problem with capitalism, in other words, is a systemic one. It has little to do with the character of individual capitalists. In fact, they, like workers, are constrained by the system. Capitalism is about structures and processes, not (primarily) morality. Inequality hasn't increased since the 80s merely because bosses have become greedier. It's because of processes such as financialization (pdf), technical change, globalization and the decline of trades unions and atomization of labour.

It is very easy for leftists to forget this (I do so myself sometimes) or not to know it in the first place and instead to adopt a moralistic account in which workers are exploited by greedy bosses and bankers. This, however, opens the door to anti-Semitism; once you start talking about greed you are only a few steps away from anti-Semitic clichés. Of course, many don't take those steps, but a few do.

Moralizing about capitalism carries another danger. It's that economic systems rarely collapse simply because they are immoral. It was the guns of the Union army that defeated slavery more than the words of Frederick Douglass. And feudalism did not give way to capitalism because it was morally inferior. The job of replacing capitalism with socialism, by this reckoning, requires much more than moralizing. It requires the creation and expansion of socialistic institutions. Bleating about morality is little help here.

It has become common in the last few days to quote August Bebel: anti-Semitism is the socialism of fools. I'd add that it's the socialism of moralizing fools.