Good start. Now, recall that the constitution granted power over navigable waterways, post offices,
and post roads, to the federal government. In other words, ALL telecommunication (known in
the eighteenth century) was to be managed by Congress, which can (and probably should)
defer details to one or more semiautonomous agencies: thus, the FCC.
Well, for the post offices and post roads, it specifically gives the federal government the ability or authority to create them but does not in any way give them the ultimate authority over all forms of them. If that was the case, the streets running to and from the post office and your house would be owned, maintained, and controlled by the federal government and not your local municipality or state government where applicable. Also, competitors to the post office wouldn't be around so FedEx, UPS, DHL and the likes would not be possible independent of the government.
As for waterways, that's actually an extraction of the interstate commerce clause and not specifically in the US constitution. I believe it was around 1824 when a conflict over licensing or registration requirements came into effect and the supreme court sided with the federal government due to the interstate commerce clause. So I'm not sure that is a real strong argument but I won't dispute it in practice.
But the big problem with all this is the semi-autonomous agencies or to be more precise, unelected political appointments not in the judicial branch but in agencies with the power to alter, create, and enforce and/or punish regulations which become laws or have the effect of laws instead of congress actually following the constitutionally provided method of creating federal laws.
Alas, Congress isn't totally clear in their guidance to the FCC (which is limited by the statutes that
created it), and the FCC has too much history to sort through, and too few options that can be swiftly
invoked. Getting the states to stop prohibiting telecommunications is very much in the
public interest, and isn't at all contrary to the Constitution.
It very much is contrary to the US Constitution. If congress has the power to act, then congress itself should act. What you are advocating for is a political appointee, independent of the US constitution and with the stroke of a pen, altering, removing, or negating state and local laws that it does not like and that you do not like without regard to any reason the state or local laws were put in place or the wished of the electorate within those jurisdictions.
If and as Congress clearly decides that e-mail (the kind of mail everyone uses nowadays)
is a 'post roads and post offices' function, they can bypass any state or even municipal
attempt to monopolize/throttle. It can also be treated as 'interstate commerce', which has
a good size body of settled law, of course, and also supports federal primacy.
If they so choose, then they should do so. The problem is, they are not doing so which is why the warning was made. It's basically saying what you do is not set in stone and can be undone just as easily so make sure you have good enough reasoning that any political appointee in the future would also support the move.