Worse, what happens when your illegal commando raid fails?

I'm sure there was a Clancy book about this. Maybe it even got made into a film!

The government south of the border has failed. The cartels have more control over large swaths of Mexico than the Mexican government does. America should not tolerate that situation. The security of our people demands the pacification of the cartels.

So if the Mexican government requests help in maintaining law and order, then fine. Otherwise it's breaking international law.

The Mexican government won't solve the problem because a large chunk of the Mexican populace is in denial about the nature of the problem. For example, every time the Mexican government tries to pass laws to more effectively wage war on the cartels--and war is the truth of the situation--you have mass civil liberties protests in Mexico City. Further, the government is partially controlled by, and even more terrified of, the cartels too. And it certainly doesn't help that the Mexican government is poor, while the cartels are raking in profits from the largest drug market in the world, the United States.

"International law" does not exist. In international affairs, there is only power. If the security of our people depends on resolving some situation in another country, then we must do it. Some worthless piece of paper with no realistic enforcement mechanism (i.e. not law) be damned.