I would hope that theory is accepted because it is what actually happened. The Nazis planned to exterminate all of the Slavs and use their land for growing food

I would hope that theory is accepted because it is what actually happened. The Nazis planned to exterminate all of the Slavs and use their land for growing food (Lebensraum and Generalplan Ost), and the Caucasus for oil. The former goal failed thanks to the Soviets putting up a good fight, the huge size of Russia, and bad weather. The latter because Hitler really wanted to defeat the Soviets at a city named after Stalin instead of just driving past it. He wasted his entire invasion force (~800,000 casualties) when the Soviets encircled and destroyed it. The Soviet commander in charge of the defense of Stalingrad, Zhukov, escaped Stalin's purges because he was stationed in the middle of nowhere, and soundly defeated the Japanese in Mongolia when they tried to invade in 1939. Japan gave up it's plans to invade the USSR for resources (permanently, as communicated by the spy Sorge, which allowed USSR to transfer all of their soldiers to the European front), and instead invade European colonies instead, which directly led to Pearl Harbor.