I have previously written for HuffPost UK about my own personal ‘journey out of Corbynism’, the experience of slowly but surely losing faith in the man who currently leads Her Majesty’s opposition. I thought I had comprehensively described the mental processes that this involved, but following this week’s downright ugly episode – the Labour Party’s rejection of the full IHRA definition of antisemitism – I have realised there is more to be said.

For rational thinking adults, understanding that racism is bad isn’t difficult. Nowadays most people realise that racism is bad long before they begin to think about economics or foreign policy, and this is part of the reason Jeremy Corbyn was initially so appealing to me. He made, and continues to make, a big thing of his anti-racism credentials, and in 2015 this stood out to me more clearly than pretty much anything else he had to say.

As I wrote in my last article on this topic, I know that there were thousands like me three years ago, young people who hadn’t spent years reading Marx or even much Chomsky, but who had worked out that racism was bad. And here was a politician who defined himself by his opposition to racism above all else (unlike those who he was running against). Supporting him made perfect sense.

This week Margaret Hodge, whose grandmother and uncle were murdered in the Holocaust, reportedly told Corbyn that he was an ‘f*****g anti-Semite and a racist’.

Now, what are we to make of this, the young liberal-minded who made our minds up about racism most probably during our teenage years, or earlier. Who, in some cases, became interested and engaged in politics specifically because of Jeremy Corbyn, and his noble stance against bigotry. How do we process Hodge’s accusation, when it jars so achingly with our own rock-solid belief in the Labour leader’s integrity?

For people like this to be confronted with examples of what Hodge would no doubt call Corbyn’s antisemitism is not like realising Father Christmas isn’t real. That is a gradual process, during which the more one thinks logically about the sleigh, the reindeer and all the chimneys, the more one becomes aware of their earlier naivety. It is in fact quite reassuring in cases like this to feel the truth of the world a little more clearly, to cast off childish, fantastical superstitions.

For some of those who, like me, supported the Corbyn movement precisely because of the man’s apparent virtue, to be confronted by what happened this week is much more like being told that black is really white, or that two and two actually makes five. The brain is not willing to budge easily in cases like this, despite the clear evidence which shows that, if Jeremy Corbyn is not truly anti-Semitic himself, he has nonetheless provided cover for, and sometimes allied himself with genuine racists.

This is why I think there are many thousands of otherwise well-intentioned young people who still support him. To have one’s core belief about someone, in particular a seemingly inspirational politician, turned on its head is to find oneself forced into questioning more than just the character of a London-based MP. What naturally follows from that is an unavoidable questioning of one’s own judgement, which might just lead to further self-doubt about other decisions made and opinions held. And there’s no doubt that this unravelling can be pretty scary. Terrifying, in fact.

It has been interesting to watch how high-profile Corbyn supporters have reacted to the issue of Labour antisemitism in recent months. In fairness to the writer Owen Jones, he has acknowledged the problem of left-wing racism, and has unequivocally condemned it, which can’t be said for all those in the Corbyn camp. But even with Jones you get the feeling that he has had to separate the far-left bigots from Corbyn in his mind.

He could not possibly begin to imagine that the current Labour leader might have any type of sympathy whatsoever for the views of these people, because any suggestion that Corbyn might, in some cases, actually be on the side of the racists, would shake the foundations of Jones’ view that he is a truly honourable man who has always fought against prejudice wherever he has encountered it.

Good, sane people enjoy healthy debate and argument, but it is a whole different thing to have one’s ostensibly grounded assumptions about people and the world seriously challenged, and it is not always the case that good, sane people are able to meet such challenges head-on.