Ignoring the specific example of Hermehditary (for now...), I'd say that using examples of pure evil in real life doesn't automatically excuse cartoonishly evil characterizations in movies, because it's a fundamentally apples-to-oranges comparison; real life is, well, real life, while movies are artificial narratives intentionally created by artists for outside audiences, and they're made up of an inumerable amount of creative decisions, both big and small, intentional or unintentional, that sends various "cues" to the people watching them.
So, there's always a certain amount of artistic "manipulation" inherent to even the greatest movies, to get us to respond the ways the filmmakers want us to, a manipulation that we're always aware of on some level as an audience, even if just subconsciously; the trick to making that work is for it to not be too blatant in its manipulativeness, which is why characters that obviously just exist to create conflict and get the audience to hate them (and get on the side of the heroes) is one of my biggest pet peeves as a movie fan, because it's lazy. Again, while really, really evil people obviously exist for real, that's no excuse to just write characters that same way, because it's like the screenwriters are trying to say "Hey, it's okay if I wrote this over-the-top, one-dimensional characterization in my movie, because there are people like that in real life!". Movies aren't real life, so that's not gonna fly with me.
Yes, that’s fair enough and a common response, but it, in turn, doesn’t quite fly with me. Not sure I can articulate why. I think depth is relative, actually. I very often sympathise with said one-dimensional evil characters because I think that their main pursuit, as with Silva, is more or less all there is left intact about their personality. It drives them. And so on. People say their job is their life and that’s a persistent problem, so for many villains, equally, the pursuit is “their job” - Blofeld runs Spectre full time, even if he does yoga on Sundays - of course we’ll focus on that.
But even if film isn’t life, my natural response is that it’s no excuse to do the opposite - create totally unwarranted resolutions. Like if a woman tells an ex in plain language in the opening sequence that the baby is not his, does it really have to turn out to be his? How about a
Hipsters (2008) kind of ending, where, oops, it actually isn’t? (Highly doubt anyone here will watch that, so).
As an aside, an approach that focuses on the unlikeable characters’ negative traits doesn’t have to be an “excuse” or labelled as such. Maybe the creator wants that artificial narrative to address exactly that, how some people can just kill a child (the banality of evil and whatnot). Anyway, I always feel there’s a cog missing in this conversation. Villains don’t have to necessarily advance plot; they can serve as a foil to the protagonist, as in the original
X-Men: First Class or whatever; they are just someone who at some point made a different choice than the protagonist.
Maybe I wouldn’t call that mother a villain if the story was about her. I’ve seen something similar, which I can’t place right now, but will do. You could very well have a story about a woman who came to do that to her kid, gradually - showing her over a couple of days, how she gets to that stage.
Christine (2016) meets
Let’s Talk About Kevin. I am the living and breathing example that you won’t necessarily hate these characters, even if they exist to be hated, because I know for a fact I’ve hardly ever hated a villain in a good narrative, no matter how one-dimensional. Even if their motivation is just being “angry”.
Edit: wasn’t sure how to phrase this earlier, but there’s also a lot of cherry-picking when it comes to such conversations. So it’s fine to have “diverse” casting in Arthurian films because we want to reflect the real-life (and real time!) demographic make-up of modern multicultural societies, but when it comes to the worst human traits and whatnot, oh, cinema isn’t really meant to emulate life, it’s all for impact. Again, I see a deliberate imbalance and disingenuousness.
Also your impassioned hatred for
Hereditary appears rather off topic. I referenced it because that’s where the topic last came up as far as I’m aware.