Yeah and you wouldn't have a major motion picture starring genuinely Adolf fucking Hitler who is framed as the protagonist who goes through the hero's journey and is constantly portrayed as a calm and rational idealist who's for true totes sympathetic.
Unless you were making some spicy new propaganda for the man, I mean. In which case you would probably also make like Infinity War and conspicuously make sure his ideals are only attacked from the baby-level "that's wrong though" "yes but it works and I must do it for the greater good" as opposed to "that's wrong and also it doesn't work you fucking grape take a look at this hard evidence that it does not" because that would shatter the mystique and make Thanos look like what he is, which is a giant purple dipshit that doesn't know how anything works.
Like, that's the issue here. Thanos' new motivation... is dumb. It's just fucking dumb. Once you prod it even a teensy bit more than not at all it falls apart, and if you did the responsible thing and actually had your characters do so then Thanos' entire appeal as a Big Strong Sad Dad Morally Complex 'Idealistic' Hard Man Who Must Make Hard Decisions is shattered in turn because suddenly you realise he's just a big purple dipshit who's never read a book in his life or indeed understands basic statistics.
This is like having a villain who's so complex and tortured and burdened by the weight of the duty he's set for himself because someone broke his four-colour retractable pen given to him by his dead parents in high school so he's going to commit genocide on all pen manufacturers until by virtue of the power vacuum left they'll be forced to produce more of this incredibly rare four-colour variant and throughout the entire movie everyone carefully avoids mentioning that you can easily pick up more of that kind of pen at any given Officeworks for under $3 a pop. And then you stay especially quiet once he reveals that his power is like Unlimited Blade Works but for pens so he spends the entire movie conjuring entire tonnes of pens out of the ether and hurling them at the heroes in ballistic ballpoint barrages.
Well that's because to Thanos, there is no other option. Because if he admitted that everything he's done up to this point was for nothing, he'd be admitting that he truly is a monster who has no remorse, that his reasoning is flawed. And he can't handle that, he refuses to belive that he's wrong, so he goes on with his plan to wipe out half the universe. The reason he seems so sympathetic is because he sees himself as a hero, righting the wrongs of the universe. It'd be pretty hard to be a hero without some sympathetic aspects to your character, when you're committing genocide.
It's why the Joker brings up his back story in the Killing Joke. He believes so hard that it just takes one bad day for a person to end up like him, and so he sets events into motion to carry out his plans to give Batman and Gordon that "one bad day." Which, depending on how you interpret the end scene, succeeded.
Thanos only mentions Gammora's planet in his monologue, but refuses to mention the other planets he's conquered. Why? Because it didn't work, because his plan failed and it was only by a stroke of luck that it worked on Gammora's planet. But he's not going to tell her that, his whole monologue is him trying to prove to himself and to Gammora that he's on the right path.
I'd doubt people like Stalin or Hitler would admit that they were wrong, they'd propagate that their plans were leading their nations into the future, making their countries great again! Of course their plans weren't working, and they died horrible painful deaths. Something I think Thanos will be acquainted with in the next avengers movie
