I mean if you want to get academic about it - I suggest you talk to some people in academia. Nearly all of those who say “Fascism is different.” self-describe themselves as Marxists or are Stalinist apologists - such as Michael Parenti or Sheila Fitzpatrick. Gee, I wonder why Marxists would want to distance Communism (and more specifically - Stalinism) from being compared with other fascists regimes like the Nazis. Maybe they don’t like how it makes them look bad?

https://en.wikipedia.org/wiki/Comparison_of_Nazism_and_Stalinism

No really - read the above link and anyone who is cited as saying Stalinism isn’t fascism check their wiki profile. Without a doubt they’re a self-described Marxist. They’re quite literally the only people who deny that Stalinism was a form of fascism and play apologists for all the atrocities that took place.

A disturbing amount of Communists see attacks on Stalinism as an attack on Communism and so make all sorts of mental gymnastics to defend Stalinism.