This is dangerous thinking; people perceived to be blocking progress - farmers, aristocrats, reactionaries - can be more forgivably slaughtered than ethnic groups because they're allegedly part of the problem, not the solution. After all, you've got to break some eggs to make an omelet.
For many, the Soviets and the Red Chinese elude the genocide charge because Communists were omelet-makers. Ukrainian kulaks, or independent farmers, opposed Stalin's plan for collectivization, so they were murdered for that "greater good."
Today, Mao and Stalin aren't in Hitler's class of evil because Hitler wasn't a "modernizer," he was a racist. Note how the Russians have no problem copping to the charge of mass murder but recoil at suggestions it was racially motivated.
It's a wrongheaded distinction. Murder is murder, whether the motive is bigotry or the pursuit of allegedly enlightened social planning.
It's also a false distinction. Racial genocide is often rationalized as a form of progress by those responsible. Under the Holodomor, Ukrainian culture was systematically erased by the Russian Soviets, who saw it as expendable. No doubt the Sudanese janjaweed in Darfur and the Chinese People's Liberation Army in Tibet believe they are "modernizers," too.
Or consider the ultimate racially motivated genocide, the Holocaust. Gotz Aly and Susanne Heim demonstrate in their brilliant book, "Architects of Annihilation: Auschwitz and the Logic of Destruction," that the Final Solution, particularly in Lemkin's own Poland, was perceived by the young economists overseeing it as a "modernizing project that would transform society."
In Germany, the effort to crush Jewry was intertwined with the effort to nationalize the economy and eliminate small and independent businesses. For German social engineers, the Jews were convenient guinea pigs for their economic experiments. The first test cases were not the Jews but the mentally ill, who were classified as an economic liability - "useless bread-gobblers" - in Germany's 1936 Four-Year Plan of economic modernization.
The climate of anti-Semitism made the Holocaust possible, but so did Enlightenment bias, which holds that almost anything can be justified in the name of progress.
I doubt such distinctions would have been of much comfort to Lemkin's 49 relatives.