I was leaning on the wall in a Soho cellar last week, idly scanning acts at the weekly Comedy Camp, when an un-comic train of thought began. The host, Simon Happily, launched into an untypical rant about his intention to boycott the “Pride” march on Saturday. As every Archers listener knows, this is one of the PC pinnacles of the year, when gay pride storms across the capital with rainbow flags, arresting outfits and flamboyant humour.

It should be a matter of quiet satisfaction that London is one of the world's safest places to hold such an event. In cities from Moscow to Jerusalem these marches have been banned or met violence. London is also distinguished by having a community ironic enough to host the Duckie collective's mocking echo entitled Gay Shame. They plan to “celebrate” rival concepts of masculinity with “the aesthetic of a giant minicab office - sticky, brown, stained, a bit pongy... no pink, no heels, no make-up, no floral patterns, no humanity”. Oh, come on - what's not to like?

But Mr Happily's rage against the main Pride march was because on the lead float will be the Mayor, Boris Johnson. Who once, musing on civil partnerships, wrote that: “If gay marriage was OK - and I was uncertain on the issue - then I saw no reason in principle why a union should not be consecrated between three men, as well as two men, or indeed three men and a dog.” Mr Happily quotes this as proving that Boris's presence makes Saturday's whole march “a travesty”.

So I started to study the relationship between Boris Johnson and this particular interest group - not because of gay issues, but because it resonates with so much else about the hysterical way we argue in this political age.

The demonisation of clever, wayward Boris throws light on our worst sickness: the politics of enmity. The bald fact is that while the jury is still out on his actual effectiveness, Boris Johnson is an intelligent libertarian with a real desire to do something practical instead of just catcalling from the sidelines. I admired him when he first stood for Parliament - less lucrative than journalism at his starry level - because with unusual shamefacedness he muttered to an interviewer that he wanted to “do his bit”. I tended to believe him. Those who write from inside glass houses, never risking electoral humiliation or boring committee-work themselves, should be careful how they throw stones.

But the new London mayor has demonstrated the perils of travelling from the commentariat to public office in a vindictive political culture. To succeed in modern politics you should take care to be a bland, self-preserving, sober, drugless, funless, dull-witted bore for years beforehand. Boris Johnson hobbled himself by being human, erratic and witty. His back catalogue of writings will follow him whatever good he does in real life: the politics of enmity decree it. In the mayoral campaign he was branded a racist merely because of two flippant expressions he once used. They occurred in pieces which, if read in full, were guying the patronising (slightly racist, indeed) way that British leaders love to escape unpopularity at home and be greeted by smiling Commonwealth ceremonial.

He was branded homophobic (though he finally voted against his party line over Section 28) because of the “three men and a dog” and a couple of equally flippant remarks. But read it with any care and you see that he was playing with the idea of mutable social values. It was clumsy - I doubt he had grasped the real argument for civil partnerships, which is social, financial and legal justice - but it was not hostile. Moreover, he has got the point since, and voted in Parliament for the new law. Boris Johnson is not a homophobe. Hedonists rarely are.

Yet during the election campaign lies were spread that he would abolish funding for the Pride march; on race and class too he was hammered without regard to truth.

A disgusting attack in The Guardian called him “this bigoted, lying, Old Etonian buffoon... moneyed creep... he has lied flagrantly, flamboyantly to save his marriage... despises people who are not of his class, which means all of us... a snob's London is a Monday-to-Thursday kind of affair behind fusty doors, in clubs that only just let women in, let alone plebs, in restaurants that don't have prices on the menus, in the Regency offices of magazines whose only distinction is that all the staff are shagging each other”.

That reads just as nastily as any right-winger's jeer at sandalled lefties or BNP rant about immigrants. Another writer used the hilariously golf-clubbish expression “he is not one of us” and a pother of petulant glitterati were wheeled out to condemn him - Alan Rickman, Vivienne Westwood, Will Self, Ben Okri, half of Mitchell and Webb, Arabella Weir - that woman who wrote “Does my bum look big in this?” - the usual bien-pensant suspects.

Feeling safe from any charge of hate-crime themselves, they called Johnson everything from racist to mad (not to mention Etonian). Arabella Weir promised that if he won she would throw herself in front of a horse, go on hunger strike and chain herself to railings. I see no reports of her having done so.

It is hate that fuels such attacks, not love of your fellow man. This Saturday those not afflicted with hate-addiction should find it enough that he now backs civil partnerships, regrets the offence and “believes in loving relationships between all sorts of people”. He will spend Saturday on a float to prove it, braving whatever they throw at him.

And some will. Once a cardboard demon is created, whether asylum-seeker or Etonian, it is not enough to attack him for what he actually does. Rage is provoked entirely by the need to be enraged. Borisophobes feed their addiction by jeering at his perceived (and entirely earned) wealth, at his accent, his education, his imaginary toff lifestyle. They are no better than any other hate-junkies: racists, bigots, Islamists and Islamophobes, gay-bashers, or the 1950s snobs who used to claim that council tenants kept coal in the bath. Putrid loathing spurts in all directions, fed by the media and opportunist politicians, and sometimes, alas, by clerics. It is all despicable.

To quote Mayor Johnson himself in an interview with the Pink Paper: “All irrational human hatreds are always really about your own feelings about yourself in some way. Anyway, I think it's all bollocks and the sooner we get over it the better.” Quite.

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