I actually believe the opposite-- that by all these quick fixes (however you'd like to go about it in this particular case), we neglect the real issue, and the more that real issue is neglected, the worse it will get. Our intemperance will just manifest itself with whatever is currently en vogue. Besides all that, however, there is the
tiny matter of personal rights (yes, this applies to corporations peddling their wares); so long as it's not addictive (yes, I'm well-aware that processed foods create something of a craving, but it's not medically defined as an addiction in the same sense as nicotine is), how can we justly stop a company from selling/advertising their product? If you'd point to the greater social good that would obtain (less obesity etc.), I could say the same for many other things, including alcohol and cigarettes. But we know how well prohibition worked out.
If you can advance a persuasive argument for curtailing the rights of companies to advertise and distribute their product, I'd certainly be inclined to listen to it-- because I don't want you to get the idea that I'm defending these companies, because I'm not. What they sell (to say nothing of their business practices) is horrible in every way. I just think the issue is a bit more complex than you give it credit for; it ultimately comes down to balancing between various groups' interests and rights. And, as in most such cases, rights > interests (so long as no addiction or coercion can be proven). In my opinion...
Imo, the biggest reason for the explosion of fast food isn't the marketing (though I agree that they increasingly target younger and younger children, who cannot make an informed decision, and then put pressure on their parents to go get some food), but rather the hectic nature of modern life, as well as the fact that families no longer eat dinner together most of the times. Though I do concede that their commercials etc. have become ubiquitous over the years.
There's no easy solution to this that takes into account the nuances of the issue, imo. I'd have to think more on it.