The feds will still go after it as an illegal drug when presented as recreational and the will keep the stigma going on forever. Furthermore it will keep a lot of talented people out of good job opportunities for smoking a joint after work instead of having a glass of wine.
The research at the time said not to ban it because it is reasonably safe for consumption and banning it would cause social unrest and distrust of the government. Check out “A Signal of Misunderstanding: The First Report of the National Commission on Marihuana and Drug Abuse”, a report from a commission created by Richard Nixon with the passage of the 1969 Narcotics Act.