As some others have pointed out, opium is not pot. Let's consider where pot comes from and whether pot money supports terrorism there:
MEXICO - I doubt it, although black market money probably lines politicians and police pockets
CANADA - unless Muslims are selling BC bud, probably not
US HOMEGROWN - terror cells? nope
Now, opium/heroin/cocaine is another matter, and some of that money may indeed go to build bombs in Afghanistan, Colombia and other places. But just for the sake of argument, let's allow the presumption that part of the pot money is going to terrorists. Now how can we stop that?
Legalization would end the black market, thereby eliminating any funding for criminals, terrorists or oppressive governments.
Of course, not using any kind of drugs is the smartest option, but one which I'm afraid is not a popular option. So, even as a conservative, I'm for letting potheads out of jail, and ending the WOsD.
Legalization would make a very grimly black market mainstream (or I might say "mainline.")