It isn't an "idea", it is a fact. Read the comment below.

From The Guardian, as mainteam leftist as one can find. And Beevor is as completely a mainstream leftist historian.

https://www.theguardian.com/books/2002/may/01/news.features11

Antony Beevor, author of the acclaimed new book about the fall of Berlin, on a massive war crime committed by the victorious Red Army.

"Red Army soldiers don't believe in 'individual liaisons' with German women," wrote the playwright Zakhar Agranenko in his diary when serving as an officer of marine infantry in East Prussia. "Nine, ten, twelve men at a time - they rape them on a collective basis."

The Soviet armies advancing into East Prussia in January 1945, in huge, long columns, were an extraordinary mixture of modern and medieval: tank troops in padded black helmets, Cossack cavalrymen on shaggy mounts with loot strapped to the saddle, lend-lease Studebakers and Dodges towing light field guns, and then a second echelon in horse-drawn carts. The variety of character among the soldiers was almost as great as that of their military equipment. There were freebooters who drank and raped quite shamelessly, and there were idealistic, austere communists and members of the intelligentsia appalled by such behaviour.

Beria and Stalin, back in Moscow, knew perfectly well what was going on from a number of detailed reports. One stated that "many Germans declare that all German women in East Prussia who stayed behind were raped by Red Army soldiers". Numerous examples of gang rape were given - "girls under 18 and old women included".

Marshal Rokossovsky issued order No 006 in an attempt to direct "the feelings of hatred at fighting the enemy on the battlefield." It appears to have had little effect. There were also a few arbitrary attempts to exert authority. The commander of one rifle division is said to have "personally shot a lieutenant who was lining up a group of his men before a German woman spreadeagled on the ground". But either officers were involved themselves, or the lack of discipline made it too dangerous to restore order over drunken soldiers armed with submachine guns.

Calls to avenge the Motherland, violated by the Wehrmacht's invasion, had given the idea that almost any cruelty would be allowed. Even many young women soldiers and medical staff in the Red Army did not appear to disapprove. "Our soldiers' behaviour towards Germans, particularly German women, is absolutely correct!" said a 21-year-old from Agranenko's reconnaissance detachment. A number seemed to find it amusing. Several German women recorded how Soviet servicewomen watched and laughed when they were raped. But some women were deeply shaken by what they witnessed in Germany. Natalya Gesse, a close friend of the scientist Andrei Sakharov, had observed the Red Army in action in 1945 as a Soviet war correspondent. "The Russian soldiers were raping every German female from eight to eighty," she recounted later. "It was an army of rapists."

Drink of every variety, including dangerous chemicals seized from laboratories and workshops, was a major factor in the violence. It seems as if Soviet soldiers needed alcoholic courage to attack a woman. But then, all too often, they drank too much and, unable to complete the act, used the bottle instead with appalling effect. A number of victims were mutilated obscenely.

The subject of the Red Army's mass rapes in Germany has been so repressed in Russia that even today veterans refuse to acknowledge what really happened. The handful prepared to speak openly, however, are totally unrepentant. "They all lifted their skirts for us and lay on the bed," said the leader of one tank company. He even went on to boast that "two million of our children were born" in Germany.

The capacity of Soviet officers to convince themselves that most of the victims were either happy with their fate, or at least accepted that it was their turn to suffer after what the Wehrmacht had done in Russia, is striking. "Our fellows were so sex-starved," a Soviet major told a British journalist at the time, "that they often raped old women of sixty, seventy or even eighty - much to these grandmothers' surprise, if not downright delight."