I'm Italian and i can tell you that the regular italian army would have surely crushed the fascist coup, the risk of a civil war was not that high (not against fascist at least), the king was afraid of a civil war against the communist and to lose power, that's why he decided to let a fascist party take over instead, because they would have never questioned his position. At the time of the march on Rome the PNF (the Italian Fascist Party) had only a few percentage of the population voting for them, so they were not considered a strong movement, and the king hoped to control them. That's why after the war the king was considered by most italian as a collaborationist of the fascist regime.
You don't have any clue of what you're talking about... in 1920-1922 there was the so called red biennium... rampant violence spread throughout Italy, coming from left-wing forces, wild union strikes, abusive occupations organized by the communist party... the risk of civil war, indeed were so high, contrary of what you wrote... all the ingredients were on the table for an imminent collapse of the country, spiraling inflation, high public debt and political stalemate: the majority of socialists didn't want to take part in a coalition with conservatives and catholics, and viceversa. So The King acted very wisely, the consent of the fascists was very high, especially among the armed forces, so the only men able to restore the order were Giolitti and Mussolini, but the first was very old and didn't want neither to come Rome and the last was a very young and energetic man.
