Being bad for you is NO JUSTIFICATION for making something illegal.
People should be free to seek happiness, even if the mechanism of doing so is self-destructive. That includes the freedom to overeat, sit around and relax instead of exercise, spend too much time keeping their skin tan, watching movies/TV that makes them stupid, and on and on.
When your pleasure-seeking causes direct and significant harm to others, THEN you have a case for making it illegal. If it only harms yourself, self-determinacy trumps the nanny-state (or should, at least).
I will add, from a completely practical perspective, that when you make highly-desired goods illegal you create black markets (because humans make lousy slaves). The black markets then funnel significant money into the hands of criminals who have no qualms about murdering people to maintain their power base. Not only must I then live with these threats, but my tax money gets spent on more law enforcement which is generally ineffective no matter how much is spent and which takes away even MORE of my freedom in order to search for crime. So...making these things illegal causes very direct harm to me...much greater harm than keeping them legal causes me (should I free choose not to indulge).