"As to the event that transpired with the two deceased people in the metro station, it was because they repressed me from broadcasting the truth." That is the simple explanation of Luis Felipe Hernández Castillo, the man who killed a civilian and a police officer at the Balderas metro stop, once the latter objected to him making paintings on the walls of the station in question.
The worry thing about all this is that the justification of his conduct that the murderer makes reflects a vision of daily life and of politics that is tremendously ingrained among the Mexicans. In fact, it's something that is taught since elementary school: the ends justify the means. That's how violence is exalted as a way to resolve conflicts with the argument that the pursuit of justice legitimizes any instrument. The torture and deaths inflicted on other human beings are the collateral and irrelevant cost before the greatness of the cause: Independence, Revolution, the struggle against tirany. As such, the walls around Congress have in letters of gold the names of people who in this age would be on the lists of the most wanted by the International Court of Justice and of human rights organizations. The reasoning is always the same: they were cruel and murderers because that was the nature of the era and because the enemy was the same. It's the same argument of those who today strike out against the rights of the rest, based on the justice of their cause. It's the argument of those who take over public institutions, kidnap busses, light cars on fire, block avenues, or set bombs: the crimes of the government are greater; the "bombs" of the government, like the fiscal adjustments, are more harmful than the bombs in banks or oil pipelines.
There may be something to the assumption, but I don't think the Balderas murders are the best supporting example, since the shooting provoked such universal horror among Mexicans. For that matter, most of the ends-justify-the-means extremism in Mexico, even that which stops well short of terrorism (i.e. takeovers of public buildings), inspires much disdain for the actors, but there's no question that a significant current of this philosophy infects Mexico's politics.
I'm also not sure that the celebration of deaths for a worthy patriotic purpose (as well as the exaltation of shady "great men") is a particularly Mexican phenomenon. I believe that I learned in high school that there were some 500,000 American deaths in World War II, but the factotum was used to show what an awesome (in both senses of the word) conflict it was, rather than a war that caused half a million separate American tragedies. Likewise for other American conflicts, including the ones far less noble, far sillier than World War II.