This relies on the misunderstanding that fascism is a movement let by individuals due to their ideals that can be prevented by other individuals with other ideals. In reality fascism is the reaction of one part of the ruling class to the falling rate of profit in which it pits one section of the working class against another in order to create a cheaper and more exploitable labor pool. Voting for the "not fascist" party doesn't solve this because the rate of profit will continue to fall and some section of the ruling class will always recognize that there is no other solution to that problem that does not remove them from power.