Selective Outrage at Evil?

A Wall Street Journal article said: "For the record, of the 20th century’s malign ideologies, Nazi ideas of who should be murdered and why strike me as slightly more odious and frightful than Maoist or Stalinist ideas of who should be murdered and why. The applicability to current U.S. events is slender, though." This confuses me. Why is mass murder because of race ethnicity/ religion worse than mass murder because of class/ economics?  Today's mass murder of people with a disability, being unwanted, or being an inconvenience seems just as evil to me.  Is there a difference in the morality of Leftist Nazis and Leftists Communists?  Both violate the Commandment, "Thou shalt not murder".  Both hate their neighbors. Neither honors their fathers and mothers. See our web for love!