One of the things I like about CGI and animation is how it makes it possible to cloak really really awful things underneath a bright glossy coat of paint.
In real life it’s practically impossible to portray a monster as ‘a nice guy really’. I think this boils down to how the human face emotes.
But CGI and animation give you only the barest hint of emoting. It takes a heck of a lot less effort to portray a sadistic psychopath in a sympathetic light. Really good animation plays with this and gets you to see yourself in the shoes of a monster.
As Mike Prinke notes, nothing about Thanos actual actions, stated motivations for taking those actions, and relationships with other characters are in any way anything other than full selfish awfulness, but the setting and bearing and artwork of the character make it easy, if you’re not really looking and analyzing behavior, to see yourself in them.
The truth is, there’s no gray area. Thanos is horrifying. Nothing he does is justified by any standard other than pure “I said so so it must be true.” Self justification is no justification. A moral gray area is when other people look at the choices you make and agree that it’s not all cut and dried.
Thanos rules by fear and ruthlessness, he’s not all that interested in morality. He has no one on his own team that can tell him that his priorities are messed up. You give him what he wants or he’ll kill you.
The movies didn’t portray him in any other way. For you to see anything else in him, you must have wanted to.
There’s an aspect of the human psyche that just likes watching people doing what they want to do and not having to answer to anyone. We all have these inner desires for that kind of freedom, the freedom to just say “fuck it, fuck you, I’m gonna do what I want and damn the consequences.” We imagine these urges to be justified, moral even. Or at the very least, that if someone could really see what we’re seeing, that they’d have made the same choice too.
But what makes a villain a villain is that they’re not justified by anything other than their own messed up head. And what makes a morality play worth watching is in the dramatic tension created by those who are tasked with stopping evil fighting not just the evil directly, but also all of the messed up logic that the evil person managed to put in their supporters’ heads.
But if a villain is morally justified in their actions, then it’s not a morality play and they’re not really a villain. It’s normal, run-of-the-mill conflict between characters.
If you want moral grey area, watch Billions. Though last I’ve watched it seems like the grey was mostly going away.
The best live-action show I’ve ever seen that gets as close as I’ve ever seen to making a villain seem relateable is Breaking Bad. Tons of people saw themselves in Walt’s shoes. I think this is because the show was able to create a veneer of super-ability with Walter having a nigh-mythic ability to make meth. So the show encourages you to see Walt as a hero and not just a protagonist. People just overlook all the repugnant decisions he makes and so entertain the fantasy.