The other one that gets me is people saying you have to have something you want to say, you have to want to write. if I give that any thought at all then I realise I have nothing to say and don't care about writing.
the trouble with putting weight on your "natural" abilities like this, "you have to be obsessed" etc, is that you ignore the fact that a good deal of your environment is dedicated to not inspiring you to care about any of these things whatsoever.
anyone who wakes up and says with a straight face "i've got something i want to say" is either a maniac or had overly enthusiastic parents. your parents, mates, partners, schools, bosses and jsa work coaches have spent your whole life conspiring to suppress your soapboxing tendencies. This is often useful to prevent you defending trenchcoat flashers at speakers corner, but its something that has to be considered whenever you reflect on the creeping sense that you might not care about something like writing as much as you'd like to.
besides the fact that if you had something you wanted to write it would already be written, the only reasonable and humane response to giving any thought to the question is, like you say, that you have nothing to say and don't really care. the wind is blowing through the trees and theres a flood in vietnam. who can write at a time like this! hang up your boots. but like many things worth doing its a process and no one cares anyway.
when you fall in love with somebody you don't automatically become a devoted doting spouse. you have to chop off limbs and change your pants and smelt yourself into a contorted new dedicated lover. you cant just "act natural".