Well, it doesn't trash the Tenth Amendment if it's a constitutional federal law, given that the Tenth amendment reserves power to the states only if the power was not ceded to the federal government. Which, in the case of regulating commerce, it was.
Secondly, the U.S. Supreme Court did rule that the federal law was constitutional, so I guess I don't understand your claim that it isn't.
Third, the Controlled Substances Act contains Congressional "findings and declarations" stating that:
4) Local distribution and possession of controlled substances contribute to swelling the interstate traffic in such substances.
(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.
So it appears as though Congress would be unable to regulate the interstate commerce of illegal drugs unless they also regulated the intrastate commerce of illegal drugs. Why would the Founding Fathers give Congress a power that the states could easily negate -- as evidenced by the above lawsuit?
Fourth, you keep referring to the "expansive" Commerce Clause. Perhaps Congress didn't always exercise this power, but it was there. Although you are correct that Congress cannot regulate intrastate commerce, they can if that commerce affects other states -- going all the way back to 1824:
"It is not intended to say that these words comprehend that commerce, which is completely internal, which is carried on between man and man in a State, or between different parts of the same State, and which does not extend to or affect other States.
-- GIBBONS v. OGDEN, 22 U.S. 1
Lastly, there is a historical reason. Prior to Prohibition, our country attempted to regulate alcohol on a state-by-state basis. It didn't work then, and it won't work today with drugs.
The U.S. Supreme Court did rule that there is a constitutional right to abortion - does that make it true?
Congressional "findings and declarations"
Those are 'evidence' only of Congress' desire for power.
Prior to Prohibition, our country attempted to regulate alcohol on a state-by-state basis. It didn't work then, and it won't work today with drugs.
The power to enact Prohibition was granted by a constitutional amendment - there is none such regarding other drugs.