That's the basis of the war on drugs. If it were about health soft drinks, cigarettes, junk food, and hard liquor would be treated like narcotics. If it were about preventing addiction, casinos would not be allowed to use cognitive neuroscience to optimize slot machines.
America, for all its prattle about freedom and individualism, is like most other societies an authoritarian collectivist state. Freedom is just a symbol, not a real thing.
You are allowed freedom within certain domains as long as you don't do anything too challenging to the "social fabric." If you do, a whole host both legal and quasi-legal options are deployed against you. Search for "cointelpro" for a good historical example. If you can't be legally prosecuted, you'll be quasi-legally or even illegally harassed and persecuted.
Alcohol is far worse than many illegal drugs, but it's legal because "normal" people use it. You can't make being a hippie illegal, but you can intensely prosecute certain things that hippies do. You can't make being black illegal, but you can do the same there -- crack and cocaine are exactly the same chemical, but crack carries a harsher sentence because minorities use it while rich white people largely use cocaine.
The reason a lot of this coalesced around drugs is that the constitution has nothing to say in that department. You can't ban religions, or speech, or styles of dress, but there's nothing in there about a right to sovereignty over your body, and the regulation of trade is explicitly permitted. So drugs, being something that correlates with certain cultures, serves as a wide open legal vehicle for attacking minority populations.