It's just that Oda wants to play both sides. He wants to keep up the façade that Luffy has no intention of saving the world, and does so each arc by having him "coincidentally" save a country as collateral, usually because he meets one or two characters and they give him something mundane. Yet at the same time, Luffy is the "good guy" and cares about the suffering of others. The problem is, that can't be his primary focus because otherwise he wouldn't be going on the selfish journey he is, he'd be stuck helping countries around the world. (In fact, due to his backstory, he'd probably be in the navy at the moment, rather than a pirate.)
Just this arc, Sentomaru didn't give him anything (and in fact he has a bad history with him), yet when Lucci butchered him he got angry.
I don't know whether you'd call it stupidity, but yes Luffy doesn't connect the dots in the bigger picture, because it's not in his nature to ponder those things. That doesn't equal him not caring about random people. Do you think if the birdcage slaughtered everyone in Dressrosa except the few characters he'd met, that he'd be equally content with the outcome? Nah.
Just this arc, Sentomaru didn't give him anything (and in fact he has a bad history with him), yet when Lucci butchered him he got angry.
I don't know whether you'd call it stupidity, but yes Luffy doesn't connect the dots in the bigger picture, because it's not in his nature to ponder those things. That doesn't equal him not caring about random people. Do you think if the birdcage slaughtered everyone in Dressrosa except the few characters he'd met, that he'd be equally content with the outcome? Nah.