Agreed. Also, someone who has naturally strong self-control and feels guilty when they "slip up" can still develop a habit of not exercising and eating junk food. That doesn't mean it's a useful habit.

Note: I think the "natural sleep cycle" problem might have more to do with social expectations than innate tendencies. For example, I work mostly mornings, including several shifts a week that start at 6 am. My sleep schedule is set at 11pm-7am, although I can fall asleep as early as 9:30 if I know I have to be up at 5:00, and I have a lot of trouble staying up for, say, parties. I miss out on most of the reputation-related benefits of actually going out with people my age...when I do, I'm usually a tired wreck by midnight. It seems to me that anyone who wanted to make more of an effort than I do to be social would necessarily sacrifice the ability to easily wake up early.