How so? I criminally simplified them, just as you have.
That’s the greatest part about villains; you can empathize them. Many of the greatest villains are really heroes who have been twisted so badly that they push past their heroics and turn to sour monsters. Darth Vader, Thanos, and countless others have left an impression on all of us because they represent the dark side (pun intended) of ourselves. Many of the best villains mirror our heroes, and want the same goals.
Plus, you don’t really get to decide who the antagonist is; that’s the plot’s job.
Whether or not you agree with Thanos (I still think killing half of the universe’s population is far too massive of a leap, Mars is a little closer) doesn’t dictate his side on the protagonist VS antagonist scale.