People can condemn whoever they want, the fact is, right wing thought inextricably involves exclusion, expulsion, segregation, and/or the superiority-inferiority of groups. Left wing thought aims for the opposite (hence the right endlessly accusing leftists of being naive for wanting things to be equal)
In the first half of the 20th century- when the extremes of the extremes took place- this became evident. The Nazi atrocities came straight from the concept of "living space" (
https://en.wikipedia.org/wiki/Lebensraum), from Mein Kampf, and from Goebbels' stated, official goals.
Maoist and Stalinist atrocities aren't a product of anything inherently left wing. Political repression and civil war aren't right or left wing ideas. You won't find any work from Mao or Stalin themselves that states or even suggests "Eliminate your political opponents and anyone close to them."