Far better plan than any of the recent candidates.
My hope with the "legalize it all" approach is that quality heroin or cocaine would drive meth out of the market.
Pretty much my view - Meth is the equivalent of bathtub/radiator gin. It's dangerous, but will get you high and is manufacturable on the sly from publicly obtained materials.
In a legal environment, I figure that most all of the motel/abandoned house/garage meth labs will go away. That's benefit number 1. Benefit number 2 is that with cheaper, easier to get meth, the Methheads will either regulate their usage a bit better or eliminate themselves quicker.
The way I see it, a lot of the damage the occurs with meth right now is due to the imprecise nature of the manufacturing resulting in impure, contaminated meth, and exposure to the various chemicals and stages used to make it in poorly controlled home labs. Both of which would be more or less eliminated under a 'meth is legal' scenario.
By the same token - I figure the same forces will occur as happened during and after prohibition. During prohibition drinkers tended to shift away from the hard to smuggle beers and wines to more compact, easier to smuggle hard liquers. After prohibition, people shifted back to wine and beer as the most popular drinks, though I believe there has been a lingering of popularity for 'mixed' drinks.
So, on average, people will drift away from things like meth and crack cocaine for other, safer, drugs.