Well, what is strange about the whole "addiction is nothing physical or chemical, but merely social" is that I thought that most of the substances one can get physically addicted to actually do alter neron receptors either by destroying them or by clogging them or changing them which all causes the brain to crave more of the substance in question to fulfill certain needs it has in terms of neural stimuli. If there were no physical addiction, why would a sudden cold abstinence of an addict cause all the physical symptoms like immense pain, puking, etc.?

I get that not everyone may always be affected in the same way, this can already be observed with caffeeine. Some can drink more with little effect, others begin to tremble after a cup. But even there the heavy users have an increased tolerance/need because synapses are altered and the brain gets used to a certain dosage. Both coffeine and nicotine addicts need a certain amount of the drug as a base level to be in the same mental state as someone who is not addicted to the drug. Which makes especially a nicotine addiction a waste of money in order to feel normal.

Now as to why people need to use drugs in the first place, well, capitalism/darwinism.
You can talk all day about what socioeconomic reasons people have to take drugs but it all boils down to capitalism/darwinism. People drink a liter of coffee every morning to perform well in a competitive job situation. People smoke to deal with the stress of a competitive job situation/exams/social interaction in a competitive environment. Other people have "failed life" and cannot deal with it and then attempt to attain the chemical bliss instead. Since poor lazy losers belong in jail anyway, the criminalization is probably the best idea.