He engaged in vigorous polemics with many members of the left-wing intelligentsia from the Vietnam War period onwards, and through his teaching had a formative impact on many Australian postwar thinkers and writers such as Raimond Gaita and Robert Manne.
In January 1942, he joined the Communist Party and spent the remainder of World War II as a member of the Free Czech Forces, attached to the British Army.
Reading Arthur Koestler's Darkness at Noon had soured his opinion of them, and he used money from his family estate to bribe officials into letting him flee to England.
Those firmly supporting him included Sydney philosopher David Malet Armstrong, who called Knopfelmacher "a man fatally ahead of his time by a few years.
[5] During the late 1960s Knopfelmacher (still lecturing at Melbourne University) became de facto academic leader of those usually associated with the Santamaria-controlled Peace With Freedom group, who favoured continuing Australian military involvement in the Vietnam War.
[6] From 1979, he denounced (especially in letters to Britain's Encounter magazine) John Bennett, the secretary of the Victorian Council for Civil Liberties, for disseminating Holocaust denial literature.
In his last years Knopfelmacher mended fences with Santamaria, who, from the early 1990s, deliberately sought reconciliations with ex-Cabinet Minister Clyde Cameron and other erstwhile foes.
His protracted, usually free-wheeling, invariably slanderous late-night telephone monologues (visited alike upon associates and, more often, antagonists) retained a mythic status for decades among Australian intellectuals, not least for their superabundant four-letter words, which evoked the heyday of Kenneth Tynan and Berkeley's Filthy Speech Movement.