I hate this argument for legalization. I also think it's the wrong way to go about it if legalization were to come to pass.
Think for a moment about the power of the alcohol and tobacco lobbies. (In Michigan it's been impossible to raise liquor taxes.) Think about their marketing power. Think about their place in our culture.
It that what we want for marijuana?
I fear that capitalism, legalization and out political system are likely to be an ugly combination.
If we were to legalize, I like Mark Kleiman's proposal to keep sale illegal and legalize people growing their own on a limited scale.