Give us a legitimate reason to keep marijuana illegal for medical and recreational purposes.

"When the President took office,he directed all of his policymakers to develop policies based on science and research,not ideology or politics.So our concern about marijuana is based on what the science tells us about the drug's effects."-Obama Admin. response
In the response,it was stated that scientists at the NIH found cannabis to be associated with addiction and other health problems. Read this article and think about it: (http://www.drugabuse.gov/publications/marijuana-abuse/how-does-marijuana...)
Science and research says it is no worse than tobacco and alcohol. The government is still looking at it from a political and historical opinion. Please give us a legitimate reason to keep it illegal or make medicinal and recreational legal on the federal level now.