I think everybody agrees these people were terrible, but I do think the way they killed people matters. Hitler created a system to exterminate people on an industrial scale. Mao wanted to feed people and didn't let his ignorance about agriculture stop him, and considered dissenting (more reasonable) voices treasonous.
Considering dissent treason (hey, Trump!) is absolutely a sign of totalitarianism and something that can lead to disaster and death, but intentionally setting out to murder millions of people still feels like a different level of evil to me.
Impossible for Americans to get distance from the internecine warfare between editors i suspect.
If you will forgive some whataboutism the British attitude to famine in India might give some context. Does anyone in the UK polity intend accepting their policy killed sixty million people over the life of British India? Oh, only two million in 1943. That's ok then..
Hell, even in solely the former case it makes a large difference depending on the specifics of the intended target of direct purposeful harm.
More generally, intent is a huge factors in evaluating responsibility & level of harm, and to a lower level so is specificity.
Western society in general has plenty who want to try these policies again because they say this time it will be different.
Hitler and Stalin resided in the same town for a while http://www.bbc.com/news/magazine-21859771