Let me start in 1930s Germany. Hitler's on the rise. But much of Germany is divided between the Socialist Party (SPD) and the Communist Party (KPD). Together, they might have blocked the Nazis.
But Stalin decreed the KPD should attack the SPD as social fascists, that is, no better than Nazis.
Moving on: 2000 Presidential election, United States. No Stalin involved. Just inherited if not genetic propensity for left stupidity.
Ralph Nader declares that the Democrats (Gore) are no different than the Republicans (Bush.)
Nader/Naderism makes enough of a difference in the election to assure Bush of victory, esp. in Florida. No, Bush is not Hitler, but the Bush invasion of Iraq is a titanic geopolitical disaster. It's not the Wermacht invading the Soviet Union, but bad enough.
Nader is not running now. But Naderism lives on.
If you think Hillary = Trump, and won't vote for her, therefore, you are infected.
Enjoy your ethical/politcal purity and too bad for the rest of us.