People tend to get hysterical whenever a loosening of marijuana laws is suggested, as if any kind of reasonable reform would lead to all-out legalization. These referendums are not intended to put dime bags and water bongs in convenience stores next to the Little Debbie snack cakes. They are intended to ease the suffering of AIDS and cancer patients. But because the federal government wants to keep marijuana illegal, doctors will just have to prescribe something to ease their patients' pain that is not as addictive or harmful as marijuana. Drugs that are far more addictive and have far worse side-effects than marijuana are stocked in pharmacies and prescribed to patients all the time, but no one has a problem with that.
People associate marijuana with hippies, rap artists, skaters and other undesirable people.
In short, marijuana has a public relations problem. The myths about the dangers of marijuana have been perpetrated in this country for years, which is why even solid scientific evidence has been unable to discredit them. It's an old anti-marijuana propaganda film made in the 1930s, I believe. You can find it in the cult movies section at the video store. Maybe they had political aspirations.