In federal court last February, prosecutors made their case against Ed Rosenthal, a longtime medical-marijuana activist known as the "ganja guru." The jurors knew the California man had more than a hundred marijuana plants growing in an Oakland warehouse when they found him guilty of felony cultivation and conspiracy charges. But they hadn't been told that Rosenthal was in fact authorized by state officials to grow the crop under a medical-marijuana law passed by California voters in 1996.

Several of the jurors, shocked to learn of the crucial information they had been denied, issued a public apology to Rosenthal: "In good faith, we as jury members allowed ourselves to be blindfolded to weigh the evidence before us. But in this trial, the prosecution was allowed to put all of the evidence and testimony on one of the scales, while the defense was not allowed to put its evidence and testimony on the other scale. Therefore we were not allowed as a jury to properly weigh the case."

Our founding fathers must be turning in their graves in disgust at Judge Charles Breyer's decision--on the rationale that Rosenthal was indicted under federal law--to bar defense lawyers from mentioning the California statute. Though many have stepped forward to criticize the verdict, including the district attorney of San Francisco and two members of the San Francisco Board of Supervisors, some legal scholars argue that Judge Breyer was correct.

As Rory Little, a Hastings College of the Law professor, puts it, "A bank robber is not allowed a defense that he was stealing money for his starving children, even if he was."

Folks, if a first-year law student offered me that analogy, I would advise him to pursue another profession. Obviously no state law authorizes bank robberies. The California law, on the other hand, mandates the production of marijuana to serve an important state policy: treating seriously ill or dying patients pursuant to a doctor's prescription.

The conflict between the general federal law prohibiting the production of marijuana and the specific California law authorizing its use for medical purposes should clearly be resolved in favor of the states. At the very least, as in the case of Ed Rosenthal, jurors should be told that the person charged with growing marijuana believed he was acting under the authority of state law, and that he cannot be fairly characterized as a major drug manufacturer. While ignorance of the law is not a defense, knowledge of state law -- and of the defendant's state of mind -- is certainly something the jury should not be denied.

Moreover, the Tenth Amendment provides that "powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people." Neither the treatment of sick people nor the regulation of locally grown marijuana for medical use is explicitly left to the federal government by our Constitution; on the contrary, these powers have been traditionally exercised by the states.

Should Mr. Rosenthal's case come before the U.S. Supreme Court, it will be interesting to see whether Justice Stephen Breyer -- the older brother of the California judge who made the foolish ruling -- will recuse himself, and if not, whether he will demonstrate that wisdom comes with age. Yet the strongest support for an appeal should come, ironically, from the most conservative members of the Supreme Court, led by Justices Antonin Scalia and Clarence Thomas.

Just a few years ago a majority of the high court struck down a federal law prohibiting the carrying of guns within a certain area of any school, ruling that the safety of schoolchildren is a matter of state rather than federal power. So it should follow from this decision that a state law seeking to protect the health and welfare of sick Californians trumps the federal marijuana law.

Still, conservative justices like guns better than marijuana. Whether their personal preferences will blind them to their own constitutional precedents remains to be seen.