I love metal but I must say, is a lot of theatricality around there. Being a tough guy in pink pajamas is hard so of course must be leather and chains and tattoos and death. I don't think "Only Death is real" is meant to be a life statement (would be too ironic) so must be a way to collect in a single phrase the values of a culture. Is a brand!
Acknowledging your death may give you the push you need to live as you want, despite society's norms but if you push it too far would be as if trying to enjoy a party thinking you will play Russian roulette between drinks and dances.