More than fantasy or even science fiction Ray Bradbury wrote horror and like so many great horror writers he was himself utterly without fear of anything. He wasn't afraid of looking uncool - he wasn't scared to openly love innocence or to be optimistic or to write sentimentally when he felt that way.
I don't think immortality is necessarily the key to understanding the world. You have to be careful with what you think you're achieving. I'm all for science discovering amazing and fantastic things about our world but I think the motivations behind it are slightly askew.