Locked in with the strains we have? How do ya figure?
Also, your first two sentences completely contradict one another. The illegal trade cannot be wiped out, yet also increase in Mexico at the same time.
I think legalization here in the US would have little effect on the cartels in the long run. They'd simply find another market for their drugs, or gouge prices in order to keep the black market viable and competitive with the legal market. If cannabis were regulated and age restricted, we like to think that would keep it out of the hands of kids... but if a demand still exists, then someone is going to take up the underage share of the market. Who will it be? Well, either the cartels or someone working on their behalf, no doubt.
The real problem is that we've let prohibition go on for far too long, and the cartels have too much power for decriminalization or legalization to have any kind of profound effects on them. Besides, even if cannabis were LEGAL it still has to come from somewhere. Making it legal or removing criminal penalties doesn't address the fact that when there is a demand for a product there must be a supply. And who controls the supply? That's right, the cartels. So now we'd have legal pot, still being supplied by these criminal groups.
In order to truly take the power away from them, we'd have to create our own supply.