There were two major reasons for the invasion of the USSR with the aim of destroying the Soviet state.

One, many German planners certainly did see the USSR as a threat. Bolshevism in the Nazi mentality was not just an alternative political ideology but an insidious homunculus invented by Jews to destroy Aryan civilizations. Both Mein Kampf and other Nazi propaganda are quite clear on this. They invented or played up a myth that communists were responsible for Germany's defeat in 1918. The Third Reich's anticommunism was predicated on the idea that Bolshevism and Jews were indistinguishable and both acted as a bacillus for a healthy racial Volk. Leaving a source of contagion like the USSR was not in the cards for the Nazi Weltanschauung. On a more immediate level, the Molotov-Ribbentrop Pact had made the German war effort extremely dependent on Soviet raw materials. The Winter War excepted, the Pact had allowed Stalin to expand bloodlessly into Eastern Europe while Germany was stuck fighting a war in Western Europe, the Atlantic, and the Mediterranean. There was a fear that crystallized in late 1940 that if Germany did not act, then Stalin would be in too powerful of a position vis a vis Germany. So there was a widespread belief within the German leadership that the USSR was both a racial and a geopolitical threat. Both of these assessments complimented and reinforced each other.

The second overarching reason was that while Hitler may have conceived of the Slavs of the USSR as beneath Aryans, he saw the land they occupied as rich in resources. These resources could be used to strengthen Germany into a global power. Mein Kampf outlined the idea of taking over this area from these racially unfit and harnessing it for the greater good of the Aryan race. Hitler did not pull this idea from the ether though. There were a number of would-be geopolitical schemers and empire-builders that imagined a Germanic empire in the East. Karl Haushofer, for instance, visualized Eurasia as a "world island" in which Germany would be the central nervous system while the resources of the hinterland east of Germany were its organs. The First World War saw the high command of the East, Ober-Ost, attempt to fashion a Germanic empire out of tsarist territory. The punishing strictures of the Treaty of Brest-Litovsk was in part an expression of these dreams. Postwar also saw attempts by veterans and Freikorps to take advantage of the Russian Civil War to set up a Germanic kingdom in the Baltic in which ethnic Germans would rule over the Baltic peoples. These dreams came to naught, but were a powerful precedent when Hitler was writing Mein Kampf.

At its very core, Nazism is not a "live and let live" political philosophy. It reduced all forms of politics into a zero-sum game in which Germany always had to come up ahead. Hitler's extreme racialism categorizes and reduces entire peoples into subordinate or dominant positions. This meant that if any state refused Hitler's call to be vassals, they soon became enemies in his eyes. This drive for domination made it much easier to conceptualize a radical restructuring of the world to suit German power. The racism of National Socialism injected a supercharged element of extremism that was not as visible in earlier concepts of Lebensraum such as Ober-Ost's abortive wartime plans. Letting the USSR be was not an option for Hitler and ran counter to all of his political instincts.