It occurred to me today that I want to see this story, soup to nuts, from the Malfoys’ perspective.
Lucius was probably always a pureblood elitist snob, but I think that’s only a red herring. When Voldemort was starting trouble up, everyone had to make a choice and Mr. Malfoy chose survival for himself and his future family. His shitty attitude after Voldemort’s initial defeat can be attributed to cynicism born of people not even recognizing why he chose the way he did—Voldemort was a mudblood, which must have made Lucius’ choice to back him especially excruciating. At the end of it all, Narcissa showed she was similarly ambivalent about Voldemort when she helped Harry trick him, after being assured her Draco was alright.
But as usual nobody let the kids in on the subtleties of the situation, and they were all worse people for not knowing. Poor Draco was probably always going to me some manner of dickwad, but being raised as he was in an atmosphere of faux fanaticism would screw anyone up.
How well known was it, among the Death Eaters, that Voldemort was a mudblood? He certainly didn’t publicize it himself, and I imagine that if any of the pureblood Death Eaters caught hint of it, they dismissed it as fake news.
I think that’s why I find the Malfoys so interesting. Of course they knew, I believe Bellatrix was even at Hogwarts at the same time as Tom, and Slytherin house used to tease him about it. But as with other tempestuous and charismatic leaders in real life, there was a benefit to disregarding that shortcoming (outwardly at least). Sacrificing small virtues for great ones, and so forth. So not so much “fake news”, as “disregard the inconvenient truth and carry on with the plan”.
Being “pureblood” is a means to an end - that end being “being better than a mass of inferiors.” Voldemort offers them that - directly - so why should they cavil at his background. A “mudblood” asking for decent treatment is an affront - but a mudblood reinforcing the Malfoys arrogance (putting them above even other purebloods - like the Weasleys who are as pure as they come) is no problem at all. The phrase “as blond as Hitler, tall as Goebbels and as slim as Göring” comes to mind.