Strawman. This doesn't apply. He would not be entering another country. The US reserves the legal right to restrict its nationals from traveling to destinations it deems inappropriate.
Of course it applies, it establishes whether the US can prevent a citizen from leaving the country.
And to inspect all vehicles leaving or entering the country. So does Mexico. And both countries can restrict where this might happen.
Which would support the allegation that they cannot stop someone walking across the border.
Try again. Wrong as usual. Here is Article 133 of the Mexican constitution:
The article is taken to mean that international treaties ratified by the senate, supersede state or federal law in case of contradiction.
Read here if you can understand spanish.
Point one. There is no Human Rights Treaty so this does not apply. The document to which you refer is NOT a treaty.
No, the declaration is not a treaty, but it was later turned into a treaty as you pointed in your second post. Specifically, in article 12 section 2 of the ICCPR, the right to exit the country remains.
Or to put it more simply, they reserve the right to control who enters AND WHO LEAVES in their very constitution.
Those conditions mean that they can stop you from leaving if you have a legal case pending, or something similar. The mexican authorities cannot stop you from leaving if you have no obligations pending.
For the Record. I know of no Constitution in the world that subordinates itself to international treaty. That would be absurd.
It is not absurd. What is the point of a country entering into a treaty if it is not willing to fulfill its obligations in it. I imagine it is the same in the US, why else would the ratification have had reservations, if it is not because it carries the weight of law. But you seem to be taking it as if the UN would write a document and it becomes law in Mexico, the senate has to ratify it.