Not worth debating what "real communism is" because those systems were real and people refer to them as communist. The point is that almost everyone in today's western political left is against authoritarianism.
Quoting that book is a very juvenile thing to do. Its very lazy and biased and meant to keep the working class from learning what communism and socialism actually mean. It has worked for a long time but is starting to lose its affect. You can only repeat this crap so many times before people start to realize donating most of their labor value to a few people isn't the only thing keeping them alive.
Moreover, two of the book's main contributors—Nicolas Werth and Jean-Louis Margolin—as well as Karel Bartosek[18] publicly disassociated themselves from Courtois' statements in the introduction and criticized his editorial conduct. Werth and Margolin felt Courtois was "obsessed" with arriving at a total of 100 million killed which resulted in "sloppy and biased scholarship"[19] and faulted him for exaggerating death tolls in specific countries.
A lot of the "deaths" were estimated via demographics. If a population grows to a total that is 1 million less than expected, its clearly because communism killed 1 million people, right?
Many observers have rejected Courtois's numerical and moral comparison of Communism to Nazism in the introduction.[16]:148[27] According to Werth, there was still a qualitative difference between Nazism and Communism, saying: "Death camps did not exist in the Soviet Union".[24] He further told Le Monde: "The more you compare Communism and Nazism, the more the differences are obvious".[28] In a critical review, historian Amir Weiner wrote: "When Stalin's successors opened the gates of the Gulag, they allowed 3 million inmates to return home. When the Allies liberated the Nazi death camps, they found thousands of human skeletons barely alive awaiting what they knew to be inevitable execution".[29]:450-52 Historian Ronald Suny remarked that Courtois' comparison of 100 million victims of Communism to 25 million victims of Nazism "[leaves out] out most of the 40-60,000,000 lives lost in the Second World War, for which arguably Hitler and not Stalin was principally responsible".[30]:8 A report by the Wiesel Commission criticized the comparison of Gulag victims with Jewish Holocaust victims as an attempt to trivialize the Holocaust.[9
Aside from conflating the far right fascist Hitler with the far left authoritarian Stalin, they want to conflate that with us left libertarians who are on the opposite end of the political spectrum from Stalin and opposite corner from Hitler. They want you to think "prisons" are the same thing as nazi death camps. Basically, everything they don't like is the same exact thing that has caused all of the worst things that have ever happened
Social critic Noam Chomsky has 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".
No one ever talks about the famines in India which were much worse than anything. When you compare the famines worldwide, you can see that capitalism exacerbated the situation. These people want you to believe capitalism prevented famines. Its all hogwash and wouldn't even be an issue in today's world anyway.