For almost a century, seven lines of reasoning have been used to outlaw marijuana in the U.S. While pot legalization advocates have worked hard to decriminalize the drug, and have succeeded in doing so in some states, the federal government continues to prohibit cannabis. Outdated public policy, racial injustice, and misperceptions about drug use contribute to the reasons why marijuana has yet to be legalized nationwide.

01 of 07 Unconvincing Advocacy RapidEye/Getty Images Advocates for legalization rarely make a convincing case. To hear some supporters of marijuana legalization tell it, the drug cures all diseases while promoting creativity, open-mindedness, moral progression, and a closer relationship with God and the cosmos. That sounds thoroughly unrealistic and too good to be true for people who don't use the drug themselves—especially when the prevailing public image of a marijuana user is that of a burnout who risks arrest and imprisonment to artificially spur an endorphin release.

02 of 07 Unfashionable Lifestyles Although people from all age groups, racial backgrounds, and walks of life use marijuana, the drug has long been associated with the counterculture, particularly with "stoners" who aren't doing much with their lives. This persistent stereotype has made it difficult for many lawmakers and voters to shore up enthusiasm about marijuana legislation. Imposing criminal sanctions for marijuana possession is viewed as a form of communal "tough love" for undesirables and slackers.

03 of 07 Lack of "Acceptable Medicinal Use" Marijuana seems to yield considerable medical benefits for many Americans, with ailments ranging from glaucoma to cancer, but these benefits have not been accepted on a national level. Medical use of marijuana remains a serious national controversy, with lively legalization debates and many skeptics. In order to fight the argument that marijuana has no medical use, legalization advocates are working to highlight the impact it has had on people who have used the drug for medical reasons. Meanwhile, highly addictive substances like alcohol and tobacco do not have to meet the same burden of positive evidence.

04 of 07 Addictive Perception Under the Controlled Substances Act of 1970, marijuana is classified as a Schedule I drug on the basis that it is perceived as addictive, with "a high potential for abuse." This classification comes from the suspicion that people who use marijuana get hooked, become "potheads," and lead lives dominated by the drug. Some users do become addicted to cannabis, but many don't. The same happens with alcohol, which is perfectly legal. In order to fight this argument for prohibition, legalization advocates have asserted that marijuana is not as addictive as government sources claim. So how addictive is marijuana really? The truth is that we just don't know, but the risk appears to be relatively low, especially when compared to other drugs.

05 of 07 Historically Racist Associations The anti-marijuana movement of the 1930s occurred at the same time that bigotry against Chicanos began to rise. A Spanish-origin word, marijuana was linked to Mexican-Americans, just as the Chinese had been stereotyped as opium addicts, and, later, African Americans were tied to crack cocaine. Today, thanks in large part to marijuana's popularity among whites during the 1960s and 1970s, pot is no longer deemed an "ethnic drug."

06 of 07 Link to Heavy Narcotics Like Heroin Historically, early anti-drug laws were written to regulate narcotics like opium and its derivatives, such as heroin and morphine. Marijuana, though not a narcotic, was described as such, along with cocaine. This association stuck, and there is now a vast gulf in the American consciousness between "normal" recreational drugs, such as alcohol, caffeine, or nicotine, and "abnormal" recreational drugs, such as heroin, crack, or methamphetamine. Marijuana is generally associated with the latter category, which is why it is convincingly misrepresented as a "gateway drug."