Its from Stalin's "Concerning the International Situation" which was USSR policy until they change it to the policy of the Popular front
From this paragraph
Firstly, it is not true that fascism is only the fighting organisation of the bourgeoisie. Fascism is not only a military-technical category. Fascism is the bourgeoisie’s fighting organisation that relies on the active support of Social-Democracy. Social-Democracy is objectively the moderate wing of fascism. There is no ground for assuming that the fighting organisation of the bourgeoisie can achieve decisive successes in battles, or in governing the country, without the active support of Social-Democracy. There is just as little ground for thinking that Social-Democracy can achieve decisive successes in battles, or in governing the country, without the active support of the fighting organisation of the bourgeoisie. These organisations do not negate, but supplement each other. They are not antipodes, they are twins. Fascism is an informal political bloc of these two chief organisations; a bloc, which arose in the circumstances of the post-war crisis of imperialism, and which is intended for combating the proletarian revolution. The bourgeoisie cannot retain power without such a bloc. It would therefore be a mistake to think that “pacifism” signifies the liquidation of fascism. In the present situation, “pacifism” is the strengthening of fascism with its moderate, Social-Democratic wing pushed into the forefront.
Nowdays its mostly used like the "unlimited genocide" as a funny line but there are still some examples of very reactionary socdem politicians so some people do still follow the "moderate fascist" position over the popular front