History

https://en.wikipedia.org/wiki/The_Black_Book_of_Communism#Criticism

[T]wo of the book's main contributors (Jean-Louis Margolin and Nicolas Werth) as well as Karel Bartosek publicly disassociated themselves from Stéphane Courtois' statements in the introduction and criticized his editorial conduct. Margolin and Werth felt that Courtois was "obsessed" with arriving at a total of 100 million killed which resulted in "sloppy and biased scholarship", faulted him for exaggerating death tolls in specific countries and rejected the comparison between Communism and Nazism...

Margolin likened Courtois's effort to "militant political activity, indeed, that of a prosecutor amassing charges in the service of a cause, that of a global condemnation of the Communist phenomenon as an essentially criminal phenomenon." Historians Jean-Jacques Becker and J. Arch Getty criticized Courtois for failing to draw a distinction between victims of neglect and famine and victims of "intentional murder"...

Noam Chomsky criticized the book and its reception as one-sided by outlining economist Amartya Sen's research on hunger. While India's democratic institutions prevented famines, its excess of mortality over China—potentially attributable to the latter's more equal distribution of medical and other resources—was nonetheless close to 4 million per year for non-famine years. Chomsky argued that "supposing we now apply the methodology of the Black Book" to India, "the democratic capitalist 'experiment' has caused more deaths than in the entire history of [...] Communism everywhere since 1917: over 100 million deaths by 1979, and tens of millions more since, in India alone."

Chapter 5 of Blackshirts and Reds is another great debunking (although it's focused on the USSR), but it's much harder for people to write off Wikipedia as a source.