As I write, a man is on trial in Canada for promoting hatred of Jews. His name is Arthur Topham and his volubility far exceeds his intellect. His website reproduces Mein Kampf, the Protocols of the Elders of Zion and voluminous material of his own in which he denounces Jewish "chicanery and conspiracy", the "synagogue of Satan" and the "fabricated fraud" of the Holocaust.

I'm a near-absolutist on free speech. I've defended in print the civil rights of such people as David Irving and Nick Griffin, and criticised the recent call by Tony Blair and Moshe Kantor (for the European Council on Tolerance and Reconciliation) for laws against Holocaust denial. Many JC readers will disagree with me on this. And, while I believe that Topham and fanatics like him should be at liberty to get on with their barren lives measured out in virulent online screeds, I concede that there's something novel in the mutation of ancient hatreds even in the free societies of Europe and North America.

Topham has a predictable defence witness in his trial. It's Gilad Atzmon, the jazz saxophonist. I was the first journalist to note (around 10 years ago) the crudely antisemitic material being espoused by Atzmon, a former Israeli. His stuff was a straightforward Jewish conspiracy theory. It remains so. His submission to the British Columbia court maintains that "the endless Jewish and Zionist attempts to refer to the Protocols as an antisemitic forgery is a tactical move that is intended to divert attention from the reality of forceful Jewish lobby groups".

I'm glad to have publicly exposed the noisome and twisted opinions of Atzmon. Yet when I did so he was a fixture on the far left. He was a star turn in musical performance and political polemic for the Socialist Workers Party, which commended his "fearless tirades against Zionism". He has since received commendation from John Mearsheimer, a political scientist who co-authored a tendentious book a few years ago called The Israel Lobby. Mearsheimer has praised what he terms "a fascinating and provocative book on Jewish identity in the modern world" by Atzmon.

The language of classic antisemitism, including the most bizarre claims, crops up dispiritingly often in the world of politics and letters. One instance I recall with particular incredulity was a cover for the New Statesman in 2002 headlined A Kosher Conspiracy? showing a Star of David piercing a union jack. (Under a new editor, the NS has recovered its bearings and become an indispensable read.) Another was the sacking of Baroness Tonge in 2010 as a spokesperson for the Liberal Democrats when she called for an inquiry into allegations that Israeli soldiers were involved in organ trafficking in Haiti. Most dispiritingly for me, as a Labour sympathiser, is the election of Jeremy Corbyn as party leader - an affable lightweight with a long history of associating with extremists.

We have new forums for expressing malevolent opinions

This is all (to coin a redolent phrase of my late friend Christopher Hitchens) an indication of how far the termites have dined and how well they've fed. The digital age has created new forums for the expression of malevolent fringe opinions. We shouldn't mistake a megaphone for a mass movement, however, or treat such toxic opinions as typical of free societies and progressive parties in which Jews play an integral part and Israel is widely admired.

At least, that's what I keep telling myself and my comrades who are apprehensive of the rise of antisemitic invective in public life.