@Blue Ink:I know you were trying to play the game where you take things to illogical extremes and we see the error of our ideals, but I'm not finding the downside to anything you describe.
I would hope that the only thing we can all agree on about taxes is that they discourage the taxed behaviour. If we could tax bad behaviour, why wouldn't we?
That was obviously an hyperbole, but the issue is quite serious.
If you accept the concept that it's right to sanction people not just for the consequences of their risky behaviors (as some of my preposterous examples suggested), but for engaging in a risky behavior in the first place, you would set a dangerous precedent, not to mention a basic social inequality. If you don't see what's wrong with that, we can stop our discussion right here.
Taxation is a milder version of the same; milder, but still equally wrong. So no, I don't agree with that at all.
Aside from my moral objections, there are a few more practical problems, among which the fact that it's not always easy to distinguish between use and abuse (alcohol and other dietary products can be used safely in moderation, for instance), then the notion that price can be a cure or a deterrent for addictions and compulsions is just weird. Finally there's the fact that substance abuse and unhealthy lifestyles are frequent (if not more frequent) among the least affluent population groups, so a flat tax would not be appropriate at all.
If you really want to tax, use progressive taxation, and use the extra revenue to finance better education (the more educated population groups are those with the lowest levels of tobacco consumption, and it's also the one that's declining the fastest), promote awareness of the risks and consequences of unhealthy lifestyles, provide accessible counsel for the early treatment of addictions, subsidize healthier food. Your pick.