Why are so many who love the English language and human freedom in mourning for Christopher Hitchens? His full-length books never showed his talents to the full – not even God is not Great, his atheist bestseller. With typical modesty – and he was always self-critical, despite appearances to the contrary – he thought that only his literary essays would be read after his death. The dominance of theory-spouting obscurantists in university English departments meant he had that field pretty much to himself, and his writing on Larkin, Powell, Rushdie, Bellow and, above all, Orwell is indeed "imperishable," to use his favourite word.

But if I may break the news to belle-lettristes as gently as I can, any aspiring author who tells publishers that he or she can make them rich with collections of essays will be shown the door, rather than a contract. Christopher Hitchens could do much, but he couldn't sway the minds of hundreds of thousands of readers by literary criticism alone.

In conversation he was the most intellectually generous man I have ever met. More writers than readers like to imagine are fretful and suspicious. They bite their tongues and hide their thoughts in case rival authors "steal their ideas". Hitchens was too much of an enthusiast for life and debate to waste time being pinched and cautious; too engaged in the battle of ideas to worry about others taking his.

When you had an argument you needed to work through or a book you had to deliver, he would sit you down, fill your glass to the brim and pour out ideas, references, people you needed to talk to and writers you had to read. You would try, and fail, to keep up and hope that you could remember a quarter of what he had said by the time the inevitable hangover had worn off the morning after.

Glorious conversation survives merely in memory of the listener, however, and there is the booze question that has to be addressed as well. The BBC's obituary was delivered by its media correspondent, Nick Higham, a ferrety cultural bureaucrat who has never written a sentence anyone has remembered. He assured the nation that Hitchens was an "alcoholic". Hitchens could certainly knock it back. But he and everyone who knew him understood his distinction between a drinker and a drunk. If he were a true alcoholic he could never have written so much, so fast and at such a high standard. Nor would he have been loved, for addicts are too selfish to love. Something else the BBC broadcast inadvertently explained was why the world feels a more welcoming place for the tyrannical and the censorious without him. Hitchens broke with the left, it reminded us, over the 9/11 atrocities and the second Iraq war. Leftists accused him of "betrayal," it continued, and quoted one who had described him as a "drink-soaked former Trotskyist popinjay". The BBC could not bring itself to add that the "leftist" in question was George Galloway, who saluted the "courage" of the secular fascist Saddam Hussein, went on to apologise for the regimes and movements of Sunni and Shia clerical fascism, and – lest we forget – led millions in demonstrations against the war to overthrow Iraqi Ba'athism without the supposedly moderate and respectable voices of liberal England uttering a word of protest against his presence.

More than any other modern intellectual, Hitchens revolted against the sinister absurdity of a time when feminists, democrats and liberals in the poor world and immigrant communities were more likely to find their reactionary enemies indulged and excused by the left rather than the right.

To paraphrase Wilde, whom Hitchens adored, "on an occasion of this kind it becomes more than a moral duty to betray the left. It becomes a pleasure." I won't give you any guff about the left leaving Hitchens rather than Hitchens leaving the left. He walked out and slammed the door with barely one regretful glance over his shoulder. He remained a friend of and inspiration to many leftish writers, but for the "anti-imperialist left" that embraced life-denying, women-hating, gay-killing Islamists, he had nothing but contempt. Its indulgence of religious reaction had ruined it beyond redemption.

For all the finality of his farewell, to divide his thought into the pre- and post-9/11 Hitchens is to miss the consistency of his writing and the true source of his enormous appeal. Hitchens's Marxism was of the romantic Trotskyist variety. He had no interest in economics – a strange omission for a Marxist, but there you are. He was, instead, enchanted by the bravery and prescience of Victor Serge, George Orwell and the other left oppositionists of the early 20th century who opposed communism and capitalism equally. Ex-Trotskyists are now among the most dishonest people in politics, but their predecessors in the 1960s still had the integrity to teach him an invaluable lesson. Leftwing dictatorships were "Stalinist" in their theology, and a true Trotskyist should have no qualms about fighting them as fiercely as he or she fought the racist and repressive regimes and ideas of the right.

By an alchemy that worked its magic on hardly any of his comrades, Hitchens developed this unexceptional thought into a loathing of party-line thinking in whatever form it took. He would no more condemn Evelyn Waugh, Anthony Powell and Philip Larkin just because they were conservatives than he would make excuses for Raymond Williams and John Berger just because they were socialists. He no more approved of Israeli oppression of the Palestinians when he was "rightwing" than he approved of Fidel Castro's oppression of the Cubans when he was "leftwing".

I cannot overemphasise how much he loathed people who stuck to a party line and tried to tell me, you or especially him what we must think; how every kind of bureaucrat, archbishop, rabbi, ayatollah, commissar and inquisitor roused in him the urge to fight.

He died too young when he had too much left to say. Those who read him knew that when we had something to say on our own account that our bosses, friends, family and colleagues would deplore, we at least had the comfort that Christopher Hitchens was on our side. If we equivocated, we would hear a laconic voice from the English upper middle class, putting our arguments better than we could, and urging us to square our shoulders and speak our minds. Read him, read anything you can get your hands on, and you will hear it still.