Let me clear something up, part 2

One of the arguments I often hear against legalization is that legalization would result in vast numbers of people who would then suddenly develop dangerous drug abuse problems.
Here’s the problem with that argument (in addition to the fact that they have absolutely no evidence to back it up):
It appears that there are three main possible types of people in terms of their relationship with recreational drugs:

1. People who are likely to have no interest in using them.
2. People who are likely to use them with discretion and responsibility.
3. People who are likely to abuse them.

Yes, this is a generalization, and there are undoubtedly shades and intersections, but follow me for a minute…
OK, clearly groups 1 and 2 are not a problem to society, right? So all we have to worry about is group 3. Group 3 is likely to abuse drugs. Now, between legal drugs (such as alcohol) and the easy ability to get illegal drugs despite the drug war, what could possibly be preventing these people from abusing drugs now?
In other words, just who are these people who are both likely to abuse drugs and yet would wait until additional drugs are legalized to do so? Is this a large group? Do you know of anyone who would qualify? Is there any way that an overblown concern for the welfare of this imaginary and miniscule population can justify all the excesses of the drug war?
Now perhaps the drug warrior will say that legalizing drugs will cause people to abuse “harder” drugs. If that’s the case then it’s an argument for the immediate and unconditional legalization of marijuana, since marijuana is less of a concern than any other drug (and we should then encourage people to move to it from “harder” drugs like alcohol).
Or maybe the drug warrior believes that there are huge portions of the population who use alcohol responsibly, but will become raging marijuana addicts if it is legalized. Right.
To recap:
Can anyone identify the millions of people in the United States who are likely to become drug abusers if drugs are legalized and regulated, but are not already abusing illegal drugs or alcohol? How many of them would there have to be to justify the death of Alberto Sepulveda?