I like this idea that Hitler's literally the worst person ever, and nobody should have anything to do with buying this car because somehow the money is the bad bit. Incidentally, it's not like money is going back to the Nazis or even Mercedes - the Allies took this car, for nothing, from the evil dead man. More amusingly, it was donated to a Veterans of Foreign Wars branch in the USA which used it for its own parades.
One of the people we mention in the opening of this article is Papa Doc Duvalier. He owned a 600 Grosser and killed roughly one in every thousand people in his own population, along with other violent assaults and rapes, with a militarised, fascist, religious police force based on Voodoo to keep himself in power. The Tonton Macoute would burn its victims alive and hang their bodies from trees.
Other 600 Grosser owners include Idi Amin (killed 0.5% of the population of Uganda), Nicolae Ceaucescu (executed for Romanian genocide), all three generations of the Kim family in North Korea (not sure I need to add anything here, especially not about the three-generations punishment, forced labour camps, mass starvation and punishment rapes), Robert Mugabe, and the truly awful Enver Hoxha (killed around 2% of the population of Albania).
But for really, really evil people you'll want to look at Josef Stalin (again, mentioned in the opening paragraphs), whose forced famine in Ukraine - Holodomor - kill an estimated 4 million people by starvation and created a total population loss of 10 million through birth rate decline; a third of the entire population of the country at the time. The Rwandan genocide, perpetrated by an entire army, reduced the population in the country by more than a third in six years, with the summary execution of the ethnic Tutsi population by the Hutu Power movement (admittedly just the last and largest part of Hutu/Tutsi ethnic murders in Rwanda) at the rate of 10,000 a day, by methods that included burning alive and hacking to death with machetes. Oh and more weaponised rape. This followed the assassination of Juvenal Habyarimana, a anti-Tutsi totalitarian dictator.
And then there's Pol Pot. The Khmer Rouge's genocide in Cambodia directly wiped out a quarter of the population. Fun fact, he had a 600 Grosser too.
So did Saddam Hussein.
And Josep Tito. In fact his car sold last year for £2.5m.
Hitler might be a particularly popular bogeyman, but when it comes to evil dictators he's not an extraordinary one who requires distinction from the others. "It's Hitler's car" isn't really any different from "it's Pol Pot's car" or "it's Stalin's car", and nobody was having kittens over Tito's car either.
It's probably worth noting that two subsequent owners were a Vegas casino owner and a tobacco magnate... like gambling and cigarettes aren't evil and have never destroyed any lives...