They were simply afraid of the unknown and therefore made it illegal.
The United States Government is spending hundreds of billions of dollars fighting something they could be making money off of. The war on marijuana from 1937-1947 cost 220 million dollars. From 1948-1963 the war on marijuana cost our government 1.5 billion dollars . Between 1964-1969 the war on marijuana cost 9 billion dollars. From 1970-1979 the war on marijuana cost 76 billion dollars. Despite all the previous spending to no avail, the United States Government spent 214.7 billion dollars on the war against marijuana between 1980-1998. These statistics add up to a total of 301.42 billion dollars from 1937-1998. That averages out to nearly five billion dollars spent every year on a dug that is non-lethal. Over 71% of that was spent from 1980-1998. Figures like these make it questionable why so many tax dollars go towards something that kills no one, helps some, and is just as dangerous as cigarettes.
Why does the government insist on spending billions of dollars every year towards keeping a useful plant off the streets? I was watching Cops the other day and I saw something that made me furious about how our system works. A man was set up and surveyed buying a twenty-dollar sack of pot. After the transaction was made, police swarmed around the man's car and, screaming at him told him, to get out of the car and put his hands up. His person and vehicle were searched and nothing other than the bag was found. This man was probably in his mid-fifties and a cancer patient. He had a morphine pump inside his body that was surgically placed there to help him with pain. The policemen asked the man how long he had been smoking and he responded saying, "just since the cancer treatment". They took him away wearing handcuffs in the squad car to the station and charged him with possession. Is this sick man our enemy? A middle-aged man who does not have much time to live so he chooses to smoke a little weed to help ease the pain? A doctor put a pump of morphine in his body.