Both democracies and dictatorships were involved, anyway. So that leaves the Shoah and the murders of tens of millions of citizens by Stalinist Russia and Maoist China as the pure fruit of dictatorships.
Mao came to power as a result of civil war, and was heavily supported by the democratically elected government of democratic USA.
Stalin came to power as a result of a 'popular' revolution.
Hitler was democratically elected.
More recently the democratically elected governments of USA and some european states have caused the destruction or near destruction of Syria, Iraq, Libya and Egypt - all previously stable, secular states - by taking their own democratic mandate as permission to impose democracy on other nations.
