Before the question, how about a few statistics? The 20th century was mankind's most brutal century. Roughly 16 million people lost their lives during World War I; about 60 million died during World War II. Wars during the 20th century cost an estimated 71 million to 116 million lives (http://tinyurl.com/ya62mrqa).
The number of war dead pales in comparison with the number of people who lost their lives at the hands of their own governments. The late professor Rudolph J. Rummel of the University of Hawaii documented this tragedy in his book "Death by Government: Genocide and Mass Murder Since 1900." Some of the statistics found in the book have been updated at http://tinyurl.com/y96tqhrl.
The People's Republic of China tops the list, with 76 million lives lost at the hands of the government from 1949 to 1987. The Soviet Union follows, with 62 million lives lost from 1917 to 1987. Adolf Hitler's Nazi German government killed 21 million people between 1933 and 1945. Then there are lesser murdering regimes, such as Nationalist China, Japan, Turkey, Vietnam and Mexico. According to Rummel's research, the 20th century saw 262 million people's lives lost at the hands of their own governments (http://tinyurl.com/lu8z8ab).
Hitler's atrocities are widely recognized, publicized and condemned. World War II's conquering nations' condemnation included denazification and bringing Holocaust perpetrators to trial and punishing them through lengthy sentences and execution. Similar measures were taken to punish Japan's murderers.
But what about the greatest murderers in mankind's history — the Soviet Union's Josef Stalin and China's Mao Zedong? Some leftists saw these communists as heroes. W.E.B. Du Bois, writing in the National Guardian in 1953, said, "Stalin was a great man; few other men of the 20th century approach his stature. ... The highest proof of his greatness (was that) he knew the common man, felt his problems, followed his fate." Walter Duranty called Stalin "the greatest living statesman" and "a quiet, unobtrusive man." There was even leftist admiration for Hitler and fellow fascist Benito Mussolini. When Hitler came to power in January 1933, George Bernard Shaw described him as "a very remarkable man, a very able man." President Franklin Roosevelt called the fascist Mussolini "admirable," and he was "deeply impressed by what he (had) accomplished."
In 1972, John Kenneth Galbraith visited Communist China and praised Mao and the Chinese economic system. Michel Oksenberg, President Jimmy Carter's China expert, complained, "America (is) doomed to decay until radical, even revolutionary, change fundamentally alters the institutions and values." He urged us to "borrow ideas and solutions" from China. Harvard University professor John K. Fairbank believed that America could learn much from the Cultural Revolution, saying, "Americans may find in China's collective life today an ingredient of personal moral concern for one's neighbor that has a lesson for us all."
By the way, an estimated 2 million people died during China's Cultural Revolution. More recent praise for murdering tyrants came from Anita Dunn, President Barack Obama's acting communications director in 2009, who said, "Two of my favorite political philosophers (are) Mao Zedong and Mother Teresa."
Recall the campus demonstrations of the 1960s, in which campus radicals, often accompanied by their professors, marched around singing the praises of Mao and waving Mao's Little Red Book. That may explain some of the campus mess today. Some of those campus radicals are now tenured professors and administrators at today's universities and colleges and K-12 schoolteachers and principals indoctrinating our youth.
Now the question: Why are leftists soft on communism? The reason leftists give communists, the world's most horrible murderers, a pass is that they sympathize with the chief goal of communism: restricting personal liberty. In the U.S., the call is for government control over our lives through regulations and taxation. Unfortunately, it matters little whether the Democrats or Republicans have the political power. The march toward greater government control is unabated. It just happens at a quicker pace with Democrats in charge.