In the case of fascism and communism, both appealed to the masses who felt that parliamentary democracy had failed them. Both promised prosperity. Fascism didn't disturb the class system as much, although there were the butchers who rose to the heights of society, and communism promised total equality not only of opportunity but of results; fascism encouraged nationalism while communism idealized an international comintern; the Nazi version of fascism glorified "racism" and race hatred, and communism boasted that there were no more distinctions.
The reality?
Fascism delivered more prosperity than communism. There was no equality under communism either: there was indeed an upper class, based on position within the party. Under fascism, the old class structure remained more or less intact, but the lower classes also became more prosperous. Communism remained nationalistic no matter what was proclaimed. Was Russia anything other than nationalistic? Was China? They were out for themselves. Ask Eastern Europeans. Yes, they put East German Communists at the helm in East Germany, but that didn't stop them from stripping the area bare and sending it all to Russia. No, communism didn't create special camps for Jews or gypsies, but they were still discriminated against, and increasingly as time went on, leading to a mass exodus. Plus, what would someone call the actions against Kazakhs, the Ukrainian peasant farmers and on and on. They weren't a holocaust?
How many were killed under each system? Probably more under Communism, if for no other reason than that it spread further. I don't think it has to do with whether one system or another is inherently more "evil".
People blind themselves according to their own ideology, usually, when looking at history.
Someone said, I can't remember who: Communism, great idea, wrong species.

Fascism is by no means a good idea in my opinion, either.
Right now in the U.S. we're seeing a fascism of the left emerging that is much more numerous and dangerous imo, because it is espoused by the more educated and elite. Sometimes I just want to shake them, and take them to Cuba, and Venezuela, and ask: This is what you want????