I'm fairly certain that the people of ISIS would be in jail if they lived in Francoist Spain, Nazi Germany or Mussolini's Italy, even if they never committed a single act of violence. By advocating for a multiethnic theocracy, they would be going against that most basic tenet of fascism that is the People and the State above all else.
Do you really think so? I'd say that the Nazi, Fascist or National-Catholic "ideological principles" would have mattered very little, in the unlikely case that something similar to ISIS was existing then. A group like that could have been better used as a combative mercenary troop, or as allies of convenience in the North of Africa and the Middle East. Racial scruples might have prevented Hitler much more than other considerations; never Mussolini or Franco. Do you know which was the religious affiliation of Franco's shock troops in the Civil War and the mounted soldiers of his personal guard? I'll give you a clue; they came from the north of Morocco. Note that Franco's regime was branded as National-Catholic.
The misuse of the words "fascist", "genocide" and "anti-semite", together with comparisons with the Holocaust, should be banned by the international law.
How much time will pass until Assad is proclaimed the new ally of convenience by the international coalition?