Also figures like Ivanoe Bonomi (Also a social democrat since he was thrown out of the socialist party for publicly disavowing anarchist violence against the monarchy) who were initially supportive of fascism until it came for them personally, and then after the war was over immediately sought to re-establish bourgeois power, played a significant role in the development of Italian social democracy.

Ironically Mussolini's communist credentials prior to the establishment of fascism meant that when the fascists initially started to make waves, some members of the destra storica (Historical right) were more eager to oppose him than many liberals and softer left wingers based purely on vibes (This ended once he actually took power), and would have done so through force of arms were it not for the king's personal endorsement of fascism. This isn't a defense of the right btw, they eagerly became participants in the fascist movement, and many of them had used fascist blackshirts as strikebreakers.
Mussolinis past as an anti reformist communist is also why he attracted people like Bombacci (The "Super traitor". One of the founders of the Italian communist party, who until the end preached of Fascism's revolutionary promise) and De Ambris (Author of the fascist manifesto and personal friend of Gabrielle D'annunzio and probably one of the most important figures in the history of Italian syndicalism) and received the pseudo-endorsement of people like Bordiga (Patron saint of leftcoms).