I didn’t claim anyone believed that the Holocaust was the only mass murder. It is the push to see it as a uniquely evil event, to trest it as a thing apart, I was referring to. The Holocaust gets way more commentary and coverage than do similar (Marxist) events.
The slaughter and displacement of indigenous peoples by settler societies is not a similar event to the above megacides but rather is mostly yet another case of farmers displacing foragers, as has been going on for 10,000 years. They are not the result of a totalising ideology wielded by a state against those under its control.