But the profit margins in the illegal drug market is largely because of the risk involved. Facing legal competition, which does not have to include that risk in its price, is effectively creating a market where legitimized producers have an extreme advantage.
Edited to add:
Also, while I have no idea as to the veracity, Wikipedia says that over half the cartels' revenue comes from marijuana, and links http://www.npr.org/templates/story/story.php?storyId=1269781... in support.
Given the high fixed costs (salaries, bribes, infrastructure) of maintaining a criminal network, I expect that cutting revenues almost in half would be a tremendous blow to their profits.
Well, it wasn't me who said it in the first place, but that aside...
"legalizing all drugs is much, much different issue."
I'm not sure I agree - this is arguably the first step on that path (if we wish to continue down that path). I agree that there will be different outcomes.
That said...
"I don't think the profits would be reduced at all, simply replaced by other products."
I'm not sure you understand how business works. For that to happen, someone needs to start purchasing substantially more cocaine and methamphetamine. If the cartels are capable of making that happen, why aren't they making it happen now?
I really don't see that any of these considerations are any different due to it being a black market - if you think they are, explain why.