This seems to be the fancy version of the argument that amounts to the impossible demand for consistency advanced by stoners everywhere. It goes like this (and we’ve all heard it):
a) marijuana is illegal
b) alcohol is worse than marijuana
c)alcohol is not illegal
therefore consistency demands that we make marijuana legal or alcohol illegal. Since we don’t do the latter, we must do the former.
We can all also quote lines like “a foolish consistency is the hobgoblin of little minds”.
The truth is that nothing is immune from history. Alcohol and tobacco are so well-established culturally for historical reasons that banning them is impossible - the consequences would be worse than not banning them (as the 1920s demonstrated). No doubt if someone only just now discovered alcohol, it would probably be banned too. But that didn’t happen and it is too late. In effect, alcohol and tobacco have been “grandfathered” out of the banning process. In a similar way (albeit in a different context) bicycles as a class get a free pass from product liability laws, notwithstanding the risks of riding them on roads, which they would be very unlikely to get if they were invented just now.
It is also important to note that heroin, etc, do not have the market penetration of alcohol and tobacco. That is part of the reason why it is possible to say of alcohol and tobacco that they cause more harm than any of the illegal drugs - the very fact of legality necessarily contributes to this.
No doubt there are those who would say that banning heroin, etc has proved as unsuccessful as banning alcohol proved to be. That is a matter of political judgment. But I am not addressing whether or what we should be banning, merely the argument based on asserted inconsistency.
To suggest that we should used evidence based science for all political decisions of this sort, as though we must look only at the research relating to the medical and biochemical consequences of various drugs and nothing else before deciding to ban them, is just perfect-world undergraduate idealism. Different drugs come with different cultural baggage that can’t be simply ignored.
There may be good arguments for the relaxation of the bans on some presently illegal drugs or for the implementation of bans on some presently legal ones. But drawing parallels between different drugs and then asserting that they should be treated “consistently” is not one of them.