Except, of course, that courts have held that a farmer producing wheat for his own consumption can affect interstate commerce, and therefore the Feds can control him.
See: Wickard v. Filburn.
Though I’m not clear on whether that precedent still holds.
Who cares if intrastate commerce affects interstate commerce? That's Congress's problem. You can put your faith in the post FDR era Supreme Court's interpretation of the Commerce Clause if you want to. But I won't give activist justices the benefit of the doubt on questionable decisions.
Here's two more excerpts concerning the limits of Congress's Commerce Clause powers from expert sources, one of them from a Supreme Court opinion since that seems to be where some people put their faith. The excerpts clearly indicate that Congress has no business sticking its big nose into intrastate commerse regardless what activist justices say.
First, using terms like "does not extend" and "exclusively," Thomas Jefferson had officially clarified that Congress has no business sticking its big nose into intrastate commerce.
“For the power given to Congress by the Constitution does not extend to the internal regulation of the commerce of a State, (that is to say of the commerce between citizen and citizen,) which remain exclusively (emphases added) with its own legislature; but to its external commerce only, that is to say, its commerce with another State, or with foreign nations, or with the Indian tribes.” –Thomas Jefferson, Jefferson’s Opinion on the Constitutionality of a National Bank : 1791.
Next, seemingly reflecting on Jefferson's words, Justice John Marshall had officially clarified that Congress has no constitutional authority to regulate intrastate commerce.
"State inspection laws, health laws, and laws for regulating the internal commerce of a State, and those which respect turnpike roads, ferries, &c. are not within the power granted to Congress (emphases added)." --Gibbons v. Ogden, 1824.