What a fucking perversion of the interstate commerce clause. The lawyers twist it to mean anything. How else do you think that states can really legalize pot now, even though that pot could stay within the state's borders the entire time? Via interstate commerce clause, they argue, because it COULD go out of state. Just like I may commit a crime one day, so lock me up now before it happens.
Mail was delivered for 160+ years in this country before the interstate highways. I never once thought "Gee, this highway is here to deliver mail". It never occured to me, because that's a benefit of the highway but not the main purpose. (I'm not saying highways aren't beneficial, but that's a seperate discussion).
The interstate commerce clause is also used to justify the civil right act of 1964. Your argument also applies to segregation as well. The question being, if I have a restaurant in the middle of nowhere and the state is fine with what I do, what right does the federal government have in telling me how to run my business. Without a broad interpretation of the commerce clause, the federal government loses its ability to affect social change. It seems one can not have their cake and eat it too. I am all for state rights but not at any cost.