"...the impossibility of winning the “war” against theft, burglary, robbery, and fraud has never been used as an argument that these categories of crime should be abandoned." (From Don't Legalize Drugs, http://www.city-journal.org/html/7_2_a1.html )
It has often been pointed out that taking prohibited drugs is a victimless crime. Your examples of theft, burglary, robbery and fraud are not.
I don't have a strong opinion about this, I'm just saying it's more complicated than victimless crime, war that cannot be won, etc. For each such talking point there's a counter-point. What will actually happen once you legalize a given substance I don't know.
The article I linked to has a lot of arguments against legalization, which, judging by the comments, the commenters didn't bother to skim through.