Can Nearly Anything Be Regulated as “Interstate Commerce”?

There's an interesting legal theory at Bitch Ph.D.:

2. He argued that Congress couldn't restrict concealed weapons in school zones. That's right; your kids' right to be safe from gunplay in the schoolyard is less important than the right of 12th graders to carry concealed firearms into school. He also argued that Congress doesn't have the right to regulate ownership of machine guns under the Interstate Commerce Act; apparently he believes that machine guns don't cross borders, people carrying machine guns cross borders.

Apparently, any action involving anything that has ever crossed a state border can be regulated. The Federal government might be able to regulate breathing on the grounds that the air crosses state borders. It could definitely regulate most meals since most food in the United States not only crossed state borders but was even sold across state borders. (I have other disagreements with the post in question, but the above claim struck me as the most inane part.)