The most eye-poppingly ridiculous claim by Proposition 19 supporters is that the ballot measure legalizing cannabis would create tax revenues for the state and municipalities if they set up such regulatory schemes. There's a variety of reasons why this probably won't happen while 'marijuana' is still a Schedule I drug under the federal Controlled Substances Act. The reason that it California won't tax cannabis is, however, certainly not the one provided by the U.S. Senator Dianne Feinstein and LA County Sheriff Lee Baca in the Mercury News.
In the article, they claim that taxing marijuana sales is unconstitutional because the Supreme Court said so in Leary v. United States 395 U.S. 6 (1969). This is emphatically not what the Supreme Court said.