TLDR: Western capitalist democracies recognize private ownership of the means of production as a central human right. Communists very specifically deny that as a human right, and fascists do not.

More:

When the USSR emerged during the interwar period, this caused a great deal of consternation on the part of western leaders. Communism was a threat to the power dynamics that existed in the US and Europe, and actual socialist and communist ideas were denied unfettered entry into the marketplace of ideas, replaced by caricatures designed by capitalists. The denial of the right to personally control the means of production was cast as a fundamental attack on democracy and the basic idea of human rights.

Meanwhile, discontented working class people in Europe were finding socialist and unionist movements ineffective in achieving their political goals. Into that stepped a new ideology; fascism. It utilized Marxist ideas about social conflict, creating a politics of infinite stakes, but it also rejected social class as the locus of social conflict, instead utilizing nationalism with a heavy reliance on re-establishing the modern nation to match the greatness of a myth infused past. By removing the focus on social class and no longer calling for the end of private ownership of the means of production, fascists found allies in the political establishment, mostly in conservative parties.

In the end, both fascism and communism are revolutionary ideologies with aims to remake the form of government in such a way to serve ideals foreign to those established by liberal democratic documents, like the US Constitution (or the Weimar constitution, for that matter) But because the fascists talk a lot about preserving cultural ideals and don't talk about seizing the means of production in the name of the people, many established government, business and media institutions are tricked into believing fascism is somehow not really a revolutionary ideology.

In the modern US, this has been exacerbated by decades of Cold War ideological indoctrination in place of education. It wasn't until I went back to college in my 30s that a professor demanded I consider the early Cold War from a Soviet perspective. It's very difficult to convince the average American that the US was as much an aggressor in the Cold War as the Soviets, but the argument is quite compelling.