JUST as it takes a thief to catch a thief, so it sometimes takes a leftie to catch out his fellow lefties. And there are few better at doing that than Peter Tatchell.
Tatchell, who is probably best known as head of OutRage, a group which specialises in spectacular non-violent direct action to highlight discrimination against gay men and women, certainly has perfect leftie credentials. He even called recently for cities in his native Australia to be given back their Aboriginal names, and much of what he does through OutRage has been similarly applauded by the Left.
Trying to have Henry Kissinger arrested for crimes against humanity, for example. That was a popular one.
Then there was the mass Kiss-In in London to highlight an absurd law which allowed gay men to be arrested for showing affection in public.
Not to mention when he recently confronted Cardinal Cormac Murphy-O'Connor during the Palm Sunday parade at Westminster Cathedral to ask why the Catholic Church protects paedophile priests whilst attacking adult homosexuals in loving relationships. Good question.
OutRage calls these events "protests as performance" and since being formed in 1990 they have come up with numerous original ways of getting their message across.
The anti-war movement, still stuck in the tedious mass groupthink of the past, could learn a lot from them.
But what makes Peter Tatchell such a tricky customer for the Left to embrace is that he has an embarrassing habit of not confining his protests to the usual targets around which the chattering classes can unite - Christian fundamentalists, the Daily Mail, America.
Rather, he has the unique idea of being equally appalled by attacks on gay people wherever they occur, even if that makes uncomfortable those whom the Left see as allies.
Hence he has heartily criticised the homophobia and Latin-American machismo of the Left's favourite pet regime in Cuba, where failure by parents to report their own children for having gay sex was deemed a "crime against the revolution". And he has campaigned actively against homophobia and misogyny in reggae and rap music, which the Left patronisingly prefers to regard as the expression of an authentic street counter-culture by young black men (though they would hardly be so tolerant of similar sentiments from white rock stars).
The same inconsistency also explains why, as he recalled last week on BBC2's Newsnight, he spent decades joining countless demonstrations against apartheid in South Africa, but now that he organises protests against Robert Mugabe of Zimbabwe - a regime which has, he pointed out, killed more black Africans than apartheid ever did, and which has made life intolerable for gay men - the Left does not want to know.
Tatchell was on Newsnight to explain his protests against the Islamic cleric Dr Yusuf al-Qaradawi, officially welcomed to London by Mayor Ken Livingstone despite being, in the words of OutRage, a "misogynistic, anti-Semitic homophobe" and "an apologist for violence against women, gays and Jews".
The cleric told the Guardian he had been misunderstood, and the Guardian, being the Guardian, did not probe too deeply.
But whatever about this particular case, Tatchell has increasingly challenged negative attitudes towards women and gay people within the Islamic community, and again the Left has been openly critical rather than supportive.
The most striking demonstration of their irritation came recently when OutRage turned up at a demonstration by the Palestine Solidarity Campaign (PSC), which has a large following in Ireland, to denounce the mistreatment of homosexuals by the PLO, Hamas and the Palestinian Authority. They carried placards saying 'Israel - stop persecuting Palestine. Palestine - stop persecuting queers'.
For this, Tatchell and his supporters were manhandled by PSC activists and accused of being "racists", "Zionists", and "CIA and MI5 agents". A later statement from the PSC further charged them with "damaging the cause of solidarity with Palestinians". All for defending the human rights of gay Palestinians.
Tatchell later revealed that he had first asked the PSC to simply raise the issue of the torture and murder of gay men in Palestine with the Palestinian authorities nine years ago, and they had not even done that much.
His conclusion is that "a so-called progressive movement [is] implying that queer lives are expendable for the sake of the greater good of a revolutionary struggle", and it is hard to see any other possible explanation for their silence.
The same hypocrisies which Tatchell exposes on the Left in Britain are just as obvious here in Ireland, where 100,000 will happily turn out to protest against the war in Iraq but the same 100,000 preferred to stay at home for decades rather than raise a squeak about atrocities committed by Saddam Hussein.
The reasoning seemed to be that Saddam was an enemy of America and Israel and therefore deserved the benefit of every doubt.
The Left is stuck in the past.
They were comfortable with the old certainties which said that everything the West represented was bad and everything those opposed to the West represented was good, especially if they were former oppressed victims of colonialism. And they have yet to adjust to the realisation that those former oppressed peoples are now some of the most virulent enemies of freedom, and that the tolerance which the Left claims to espouse is anathema to many of those they champion.
It is no wonder they do not like being reminded of their selective blindness by Peter Tatchell. He really does stand for what they like to think they stand for, but he does it with courage and consistency.
Consistency is not always a virtue, of course, and Tatchell can be a pain.
But if you're going to be a single-issue fanatic, then the issue of the right to express your sexuality without being tortured and murdered for it surely isn't such a bad one.