In a lengthy key-note speech to the dinner, Harper took aim at Russian President Vladimir Putin and past adherents to communism.
"During the 20th century, communism's poisonous ideology and ruthless practices slowly bled into countries around the world, on almost every continent," Harper said.
"The result was catastrophic. More than 100 million souls were lost — an almost incomprehensible number."
The evening's goal was to help raise money for Tribute to Liberty, which aims for a permanent memorial in Ottawa to communism's "hundreds of millions" of victims.
In 2010, the Conservative government said it would support the monument.
Future generations of Canadians, Harper said, must be reminded that peace was earned through struggle and sacrifice.
In language reminiscent of the height of the Cold War, Harper lambasted communism and oppressive or even murderous ideologies.
"Evil comes in many forms and seems to reinvent itself time and again," he said.
"But whatever it calls itself — Nazism, Marxist-Leninism, today, terrorism — they all have one thing in common: the destruction, the end of human liberty."
Canadians, the prime minister said, are well aware of that destruction.
"We feel this pain so acutely because nearly one quarter of all Canadians were either held captive by communism's chains or are the sons and daughters of those who were."
He repeated his support for Ukraine, and lashed out again at Putin, saying the president has "grown more comfortable with confrontation" and Russia's "expansionism and militarism" threatens global security.
Canada, he said, has been a haven from those fleeing oppression.
"Instead of communism's grim determinism, they found Canadian opportunity."
Harper said Canada and the West played their pro-freedom role during the Cold War, and he singled out former prime minister Brian Mulroney along with ex-British PM Margaret Thatcher and former U.S. president Ronald Reagan.
The PM did express "immense regret" that Canada had not always lived up to its high aspirations.
A jury will be selecting the winning monument design team within months.
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