one word: chavez
I agree - Chavez is no doubt encouraging it. This is exactly the technique used by FARC in Colombia, and everybody knows that Chavez has been very helpful to them and given them safe haven across the border.
By the way, Mexico has been under heavy attack by its own and the foreign left for some time now. Chavez tried to influence the elections last year and there was a diplomatic incident over it where VZ’s diplomats were expelled. Supposedly, VZ military also turned up in Southern Mexico at one point, although I can’t confirm that. In any case, one of the biggest problems Mexico has is its violent left, which tries to undermine any reform or progress made in the country. Now it looks as if they’re moving beyond undermining and getting into sabotaging. (Of course, this would also benefit Chavez and other leftists who control supplies of natural gas, such as Morales.)