A reader writes:
"Since when did the federal Congress have the right to micro-manage what school-kids get from snack machines?"
Answer: Since childhood obesity has led to such an explosion in life-long healthcare costs which have become an enormous (no pun intended) strain on the U.S. health system, economy, and, yes, the tax-payers. As long as the American people have to pay the bills for children who aren't provided any healthy eating options, they have a right to try to lessen the burden.
Phrased another way using another situation, the possiblity of gun violence in schools potentially threatens the quality of education that children receive. In turn, this means they are less-prepared for the challenges of the real world once they leave the educational system. Therefore, there is a suggestion that these people could become a burden on our economy (which threatens interstate commerce) as opposed to being productive citizens. So long as the American people have to shoulder this burden, they have a right to lessen the burden. Federal legislation prohibiting guns within a certain distance of a school zone is representative of the American people's right to lessen this burden.
Now, I may not be 100% accurate on the arguments made regarding the Guns Free School Zone Act, which was struck down as unconstitutional by the Supreme Court in United States v Lopez in 1995, but I think it generally shows how the same sort of "Six Degrees of Kevin Bacon" reasoning that leads people to believe that federal intervention can be justified on any possible grounds (the courts have done us no favors by buying into this (see Wickard v Filburn).
Also of note is that the woefully positivistic view of "rights", where left-wing nanny-staters, like their right-wing nanny-staters believe in a "right" to use "powers" wherever and whenever they see fit.
It would not be so annoying if it was not a dominant strain of thought amongst the American populace.