There's been a lot of talk as of late of taxing junk food as a form of "fat tax". The basic notion is that making empty calories more expensive will reduce the economic capacity for people to consume them. In particular, it is meant to discourage the overweight from consuming them with such frequency and in high volume.
There are a lot of good reasons to oppose such a move. One is that it is essentially a way of having the government manage lifestyle, but the truth is that we already do that by taxing cigarettes. It's not like there isn't precedent for the government making lifestyle choices that are tantamount to vice more expensive than those which are considered a virtue.
Another good reason to oppose such a tax is that it will have a negative impact on the sales of the companies which purvey such snacks. They will lose money and people will lose jobs in turn. Since many food products are produced domestically (unlike durable goods), this would essentially be taxes used to undermine American jobs and profits.
Personally, I don't think people are fat because of the presence of junk food. I do believe that people who are fat almost certainly eat too many things which are not good for them, but I don't believe that the core problem is related to the presence or absence of tasty, cheap empty calories. As I have said before, I believe the problem is a mixing of biological and psychological issues which are tied up in genetics, maternal eating habits during pregnancy, endocrinology, neurological chemistry, and issues related to comforting oneself with food. If you take away the capacity to eat garbage, people who have the inclination to be fat will simply "find a new drug". That is, they'll overeat in some other fashion.
That being said, since I don't believe junk food is the main cause of obesity, I say, "bring it on." While I don't believe the tax will solve the problem in any way, I think that there may be value in implementing such a tax so that it can be seen to fail to have results. At the very least, if revenue from such a tax were used to help get at the core issues which affect overweight people, it may have some benefit. With any luck though, a failure of such an initiative might spur further research into the deeper and less shallow roots of the problem.