Hitchens is very good at cataloging the effect of Leftism on British culture, but he does have weird views. Hitler most certainly could have been stopped early on as the German army was much weaker than Hitler’s confidence made it look. The German Generals didn’t want war and warned hitler repeatedly that they were too weak to withstand a concerted effort by the Allies.
Hitler's biggest blunder was declaring war on the United States for no cause. No other nation except America could have bombed their war machine or posed enough of a threat to invade France to dilute his forces.