Marijuana Damages Your Brain
The Mary Study shows us alterations in the brain from marijuana. I have seen similar studies on fat, sugar, salt, caffeine, nicotine, and alcohol. We have discovered that Tylenol affects the brain. Ibuprofen can cause EXTREME damage, including permanent brain damage. Over-the-counter antacids and emergency contraceptives can cause permanent organ damage, sudden death, and a bizarre and frightening variety of issues.
The danger of living is unquestionable. There is assumed a 100% mortality rate for living. What is at stake are the very underpinnings of a free world. At best count, about 30% of your friends and neighbors will buy and use outlawed substances, regardless of the law or consequences. The two largest threats due to drugs are the United States Government violating your rights and or killing you, and the powerful Drug Cartels which we create - by incentivizing a black market trade.
The cost in human life for the drug trade is millions of people south of our border. Millions of people here are imprisoned, and the market is filled with unregulated substances. If you need evidence as to how destructive the ban an marijuana is, do a Google Image Search for Spice (synthentic Cannabis), Krokodil and Bath Salts. Consider - which would you rather deal with, Heroin, or Krokodil? Bath Salts or people taking pseudofed? Fake weed, with all it's side effects, or something which humans have been cultivating, eating, and producing for ~5,000 years?
Marijuana is soooo minor.
You have an excellent case for this: DO NOT USE DRUGS.
You have no case for "We should take your money, property, liberty or life for using drugs". Particularly in the case of marijuana. So, hop on the bandwagon. Stop saving people from themselves with guns and prison, and start encouraging people to make good decisions.