Thomme, in case you missed the post by publius42, followed immediately by my post, this is an issue of Interstate Commerce.
In passing the Controlled Substances Act (CSA) of 1970, the Congress declared its interest in controlling the interstate trafficking of certain substances.
§ 801. Congressional findings and declarations: controlled substances
The Congress makes the following findings and declarations:
(1) Many of the drugs included within this subchapter have a useful and legitimate medical purpose and are necessary to maintain the health and general welfare of the American people.
(2) The illegal importation, manufacture, distribution, and possession and improper use of controlled substances have a substantial and detrimental effect on the health and general welfare of the American people.
(3) A major portion of the traffic in controlled substances flows through interstate and foreign commerce. Incidents of the traffic which are not an integral part of the interstate or foreign flow, such as manufacture, local distribution, and possession, nonetheless have a substantial and direct effect upon interstate commerce because—
(A) after manufacture, many controlled substances are transported in interstate commerce,(4) Local distribution and possession of controlled substances contribute to swelling the interstate traffic in such substances.
(B) controlled substances distributed locally usually have been transported in interstate commerce immediately before their distribution, and
(C) controlled substances possessed commonly flow through interstate commerce immediately prior to such possession.
(5) Controlled substances manufactured and distributed intrastate cannot be differentiated from controlled substances manufactured and distributed interstate. Thus, it is not feasible to distinguish, in terms of controls, between controlled substances manufactured and distributed interstate and controlled substances manufactured and distributed intrastate.
(6) Federal control of the intrastate incidents of the traffic in controlled substances is essential to the effective control of the interstate incidents of such traffic.
(7) The United States is a party to the Single Convention on Narcotic Drugs, 1961, and other international conventions designed to establish effective control over international and domestic traffic in controlled substances.
If you read the above carefully, you will see that the Congress is claiming complete jurisdiction and control over both interstate and intrastate traffic in controlled substances.
This was upheld in 2005 in a California medical marijuana case that came before the Supreme Court of the United States (SCOTUS). That case was Gonzales v. Raich. You can read it here
Until such a time as this line of cases are overturned, lobby the Congress to move medical marijuana out of Schedule I classification onto Schedule II, III, IV or Schedule V.
Currently all Schedule I drugs are deemed by the Congress to have no medical purpose and are highly addicting.
Whether any of this makes sense to you or not, it is the law.