It's such an odd thing. I don't think I've ever heard people refusing to say Stalin or Hitler's names. Andrew Jackson isn't alluded to with euphemisms, despite being a piece of shit who perpetrated genocide among other crimes. Nixon doesn't get this for his crimes and shitty policies, nor Truman for the a-bombs or FDR for mass internment of American citizens.
It seems like an idea people got from Harry Potter refusing to say Voldemort.