I love how instead of becoming jaded, Luffy, if anything, becomes more sympathetic to people's struggles as the story goes on. He just left a country that was enslaved and starved and beaten down for 20 years, getting to know their individual and group suffering intimately. Something like that could crush another character. But Luffy never had rose-tinted glasses for the world in the first place, so it doesn't pose any existential crisis for him. "It's unrealistic. People die" He said about Vivi's hopes in Alabasta.

The next person he meets, after Wano country, tells him her father was turned into a mindless, living weapon. He looks so sad. He apologizes persistently for having initially reacted in enthusiasm to hearing her father became a cyborg. He's so sorry he learns her name. Which I suppose is only meaningful to people who have read/seen the whole story and know just how bad he is at learning names, and how little he cares for them on principle. It's just such a good moment.