> Aside from DUI risk and passive smoking, most of these risks are specific to the person. I can't catch obesity from being in the same room as...
That's not entirely accurate. Human behavior is effectively viral (per any of the Jonah Berger books among others). What we see becomes the norm, a behavioral norm.
Smoking has decreased because it has become "less fashionable." And so on. So while you might not catch obesity in the strict virus sense, if you're exposed enough, that exposure can and often does influence your behavior.
That's not entirely accurate. Human behavior is effectively viral (per any of the Jonah Berger books among others). What we see becomes the norm, a behavioral norm.
Smoking has decreased because it has become "less fashionable." And so on. So while you might not catch obesity in the strict virus sense, if you're exposed enough, that exposure can and often does influence your behavior.