The cartels are caused by US policy, not Mexico's. The Mexican war on the cartels is a response to the cartels killing Mexican citizens and terrorizing large swaths of the country. A country is supposed to defend its citizens - that is why taxes are paid.
Rather than give immunity to the cartels for terrorizing the citizens he claims to protect, he ought to petition the US to legalize drugs.
It's clear to me what the source of the issue with the cartels is and where all the money comes from.
That said you are mistaken about the source of the war on cartels by Calderón. There was one single relatively new cartel who was doing more than drug dealing (meaning extorting people and kidnapping mainly). And that cartel operated in the north east of the country (Tamaulipas and Nuevo León, mainly which is where I have lived for the last 10 years). These guys were particularly violent as their founding members were ex military, special forces trained by the Mossad. Calderon decided to push for an all out war on all cartels, however investigations done by some journalist argue that the war was being fought in favour of one of the cartels: El Cartel de Sinaloa, which is the one led by El Chapo. This decision didn't really make sense as history has proven, for example in Colombia, that these tactics don't really solve anything in the long term.
Both Vicente Fox and Calderon (presidents elected on 2000 and 2006) are from the same right wing party. During Fox's mandate El Chapo escaped prision for the first time. The goverment was not able to provide a satisfactory explanation of how that happened. El Chapo was caught again only after the current president Enrique Peña Nieto took power (he is from another party). El Chapo escaped again, this time through a very sofisticated tunnel, and was later caught again and finally he was extradited (something that didn't happen before, some people argue that it was because he had an agreement with the goverment).
In any case, Calderon's all out war brought Mexico years of violence that was never seen before with hundred of thousands of deaths, many of them innocent civilians. At the end, nothing changed other than the rebranding of some of the cartels such as Cartel del Golfo.
You could say that one of the reasons Peña Nieto won the 2012 elections was because people were displeased by these results. Many argue that Peña Nieto won because of fraud and because Calderon's party made an agreement with Peña's party to keep Lopez Obrador out of power. This time around it seems that they couldn't reach an agreement as Anaya (the right win party candidate) took an scorched earth approach and publicly went against the current president, eliminating any possible chance of building an alliance.
Regarding Lopez Obrador's standing regarding legalization: He said that he would put it to vote by the population of Mexico which to my mind is the correct approach. I'm pro-legalization however I think the whole country should be able to participate in making such a decision. Given that Lopez Obrador is a left wing candidate and it's the first time the Left has won a presidential election in Mexico's history (Mexico has been independent since 1810 and it abolished the last dictator in 1910, as you can see it's a very young nation).
Lopez Obrador is all for democratic countries making their own decisions so there is no way (nor need) that he will ask permission to the US to legalize. I would be appalled and very offended if he did and I'm sure the majority of Mexicans would feel the same.
The intention of giving amnesty is purely in the interest of the future of the country. I agree with him that it is an option that should be evaluated.
I'm happy to answer any questions that you may have.
