Wickard cited Shreveport as precendent, but IMHO, they turned it upside down.
The Shreveport decision states :
by reason of its control over the interstate carrier in all matters having such a close and substantial relation to interstate commerce that it is necessary or appropriate to exercise the control for the effective government of that commerce.
In other words, what is relevant is that they are registered carriers of interstate commerce. Whether there was any incidental effect on intrastate commerce was irrelevant.
In Wickard, they turned that application upside down. Whether Roscoe Filburn was a registered carrier of interstate commerce became irrelevant, that there had been some effect on intrastate commerce was presented as the relevant effect of the decision.
What was declare to be irrelevant in one case was cited a relevant precedent in another. What was explicitly declared to be the relevant issue in the first case was completely ignored in the second.
“Whether there was any incidental effect on intrastate commerce was irrelevant”
You have it backwards here, and I’ll tell you why. It’s not that the law had a sideffect on intrastate commerce. The feds wanted to control prices on interstate commerce but realized that the railroads got around this by charging different rates for travel within the states. So in furtherance of the goal of controlling interstate rates they extended their power to apply to intrastate rates. This was not “incidental;” it was a deliberate extension of power to a realm it had been in before (though it was inspired in my opinion by Gibbons, as I said).
Now not only would interstate commerce be regulatable, but commerce that directly affected interstate commerce would be, too. It’s a hop and not even a skip and a jump from there to non-commercial activity which substantially affects interstate commerce being regulatable. Wickard didn’t turn the Shreveport Rate Cases upsidedown; it merely extended the logic a bit.
Them being registered federal carriers is a red herring, by the way. Just because they carry passengers and freight across state lines does nit mean you write whatever laws you want covering their intrastate activities. You couldn’t have, for instance, mandated they offer so and so dollars an hour to their employees any more than you can order them to charge a certain rate on intrastate lines.
Notice how cleverly your bold faced quote specifies how “necessary” regulating rates on lines substantially relating to interstate lines is to the interstate regulatory scheme as a whole. Perhaps, but then again what if the regulatory scheme they have in mind is unconstitutional? Regulating prices intrastate is not necessary to regulate prices interstate. Regulating prices intrastate may be necessary to regulate interstate trips the whole way. But who said the feds can do that?
To a realm it had never been in before, I meant.
About your idea that Wickard turned Shreveport upsidedown, I’d like to clarify your confusion derives from the inappropriate inclusion of the registered carrier red herring and the mistaken attribution of “incidental effect.” Varying rates interstate lines was not some bug the perfectly constitutional interstate price regulation scheme accidentally stepped on. It was a major hurdle the feds had to jump over or blow through to achieve their dream of getting the railroads under their thumbs and stopping “predatory pricing.”
But like I asked: who said they could do that? In order to they had to exercise undelegated power. That it was necessary for the scheme is obvious, but not so that it or the scheme as a whole is proper. Hence their falling back on the intrastate price being substantially related to the interstate price. Which you say is because they were registered interstate carriers. But no matter, because intrastate commerce is not interstate commerce, even if done by registered interstate carriers.
You miss the forest for the trees focusing on the registered carrier thing. Why Wickard did not turn Shreveport on its head, and why it merely extended it a bit is that just like substantially affecting interstate commerce does not constitute being interstate commerce, being substantially related to interstate commerce is not to be interstate commerce. No matter whether you’re a registered carrier or not.