First you said it was illegal, now you're saying it's immoral. Your reasoning has just turned into opinion. Tax WILL make people pay attention, even if it's just proposing a tax, people will get worked up. That's not an opinion. Don't get me wrong, I don't want to pay a government tax on food when I don't get to choose what is and what isn't good but it will show the clueless people a little bit of what's going on.
On a related note, I'm happy as a clam paying sales tax for my state. I see my money in the roads 
Is is not true that congress does not have the power to change or persuade the change the market? Nowhere in the constitution does it give them the power to do such a thing. Therefore, it would be illegal to do so.
Also, I wouldn't say it is immoral, but more along the lines of people should be able to choose to change themselves, not have the government try to persuade them into changing while hurting everyone else who does pay attention tot heir health.
@Dann
despite the many times your reasoning ends up changing further down the discussions, without you realising it.
How did my reasoning change? I have been saying close to the same things the entire time.
More often than otherwise, your opinions too, hold very little to no weight, yet you somehow manage to stick by it
How do my opinions hold no weight? You have yet to provide any evidence for me being wrong......