Johnny,
I think what Hpslugga and I are discussing is getting at the heart of the issue, which is how a government justifies itself, or whether it is justified at all, in pronouncing on issues like marijuana.
But I'll play along: Do you think that legalizing marijuana would reduce cost?
I'm not sure that it would. We would still be involved in fighting drug trafficking with other drugs, such as cocaine and heroin and meth. These drugs would still be huge money-makers for criminal gangs both inside and outside the United States.
Nor is it clear to me that these gangs would be shut out of the marijuana industry, since they would be able to avoid the FDA entirely and thereby undercut the legal suppliers. They wouldn't be subject to whatever THC limitations were imposed. The legal suppliers would be subject to all these rules, and they would produce a product that was probably safer, but which had also now lost its subversive force. In other words, don't be shocked when the kids start to refer to the illegally produced marijuana as the "good stuff".
What we would succeed in doing, were we to legalize marijuana, is to push the threshold of subversive activity into ever greater degrees of depravity and perversion. I'd rather keep it where it is now.
The other thing we would accomplish, in terms of cost, is to create a new arm of bureaucracy dedicated to the management of the drug for public consumption. This new bureaucracy would incur cost that could not be offset by fines and court fees at the local level.