Good luck having a rational debate with druggies on this. The failure of the war on drugs starts with weed, which is supposed to be a soft drug (basically the same as drinking a beer). Its widespread consumption and inevitable legalization always has the same effect on people, it makes them lazy, complacent and horny (to a disturbing extent). Every user will argue that it doesn't have the same effect on them that it has on 99% of people using it. They are always the exception.
Another factor is that the THC content of cannabis has dramatically increased since it was first introduced. Originally, the pot that people smoked in the 70's had a THC content of about 8%. Today a 20% THC content is normal, some product go up to 30%. At this point, it's not a class C anymore. You can add edibles and synthetics product to the mix and you can imagine the consequences of widespread use.
The argument that weed = alcohol is also completely fallacious. European populations have developed a natural tolerance to alcohol over millennia. After the fall of the roman empire and up until the industrial revolution, nobody in Europe had access to clean water and we didn't understand germs and bacteria. Drinking water was often a death sentence so as a result, you would be drinking alcohol (usually cider) from the day you were born to the day that you died. As a result of this, only individuals who could adapt to this diet and function with alcohol were able to survive and reproduce, No such adaption was at work for other mind altering substances such as those derived from plants found in other cultures. This also explained why liquors had such a devastating effects on native Americans populations.
Drugs may have had some positive effect on societies in the past for where they acted as a stimulant to increase productivity (eg, cocaine was given to workers who built the American railroad system), but an argument can be made that this is not relevant anymore. A lot of post industrial societies are heavily welfarized and when you combine welfare + Internet access, you get autism and degeneracy.
The war on the "war on drugs" is a by-product of the era of liberal leftism that characterized the 80's and 90's, once the Woodstock generation took over from their parents who also didn't give a shit. Abandoning the war on drugs was a mistake. We created a generation of pothead gooners, crackheads and fent users. No drugs should ever be legalised. They turn women into prostitutes and men into fags.