I don't think he cares about humanity, I think he's a techno-utopian but it's not due to his will to better humankind it's because he's a tech bro that enjoys innovation. Those two concepts might cross over but I don't think there's any empathy in his decisions he's a sociopath.
To be honest it's the same with Bezos, Zuckerberg and Gates they've all been at stages where their driven selfish personal goals happen to coincide with (arguable) benefits to mankind.
He's an Ayn Rand character personified and like most super rich folk they end up finding altruistic projects are the final remaining option for stroking their ego. Musk probably thinks he's being altruistic with some of his projects but he's still just a rich egotistical ball bag.