Reddit reviews Mussolini in the First World War: The Journalist, The Soldier, The Fascist

In fact, it was necessary.

Fascism, as an official designation, commenced around 1919 in Italy, with the founding of the Italian Fascist Party (originally called the Italian Fasci of Combat). 1919 was also the first year a US President used an electronic PA system, when Woodrow Wilson addressed a crowd of 50,000 people in San Diego. Prior to the development of vacuum tube amplification technology, a public speaker could only have made himself (or herself) heard by shouting.

EDIT: To clarify, there was a solid precedent for loud and passionate speechmaking, even after microphones became commonplace. There was also a precedent for calm, stage-voiced speaking with very crisp diction. Because fascism depended strongly on passion (as opposed to reason) to sway common opinion, fascist speakers shouted more than their fellow politicians with a calmer agenda. But fascists were certainly capable of making speeches without shouting: here's one of the earliest sound films of a head of state, Mussolini addressing the American people in English.

Sources: Mussolini in the First World War by Paul O'Brien (Bloomsbury, 2005); Breaking the Heart of the World by John Milton Cooper (Cambridge UP, 2001).