But by that logic alcohol should be banned completely...
For example, I can buy a car and I can buy alcohol. I know that I can consume a certain amount of alcohol and once I consume more than that amount, I am likely to be intoxicated and therefore unable to drive legally.
However, if I just have one beer then I can drive home legally.
If I get hammered, drive home, crash and get arrested then it's my own fault.
It's called taking responsibility for your own actions...