In the Southwest, Mexicans were immigrating illegally in large numbers, taking up jobs that should have gone to Americans (in their opinion) and building shoddy neighborhoods, ruining the scenery. The locales resented this and demanded that the federal government make marijuana illegal, which a significant proportion of the illegal immigrants happened to use. The Marijuana Tax Act was passed as a result. It doesn't sound so bad, except the government wouldn't actually sell the stamps, effectively outlawing marijuana. The Mexicans who continued to use it were jailed, and a massive government propaganda campaign was launched in support of the motion so that people wouldn't be too bothered that it was an unconstitutional act.