Personally, I do not think armed unionist would stop hitler whose ascent to power was through elections and para-parliamenatary maneuvers and the monumental shortsightedness of german left. The counterfactual to that is Spain, where left commandend significant fire power in addition to electoral victories. Nonetheless, Franco did "pasaran."
Italy, OTOH, is a different story. Unionists shooting back at the fascist thugs might have changed the course of history there, no?
wojtek