I don't want to disparage either the pastoral letter or its author. I think much of what is written here is remarkable.
I would like to point out that pastoral letters and encyclicals tend to be ignored by many (if not most) people. I think that's at least partly because their authors don't put themselves and their values at sufficient risk to challenge the status quo. 
In many parts of Latin America, the poor use a general strike as a lever  to draw attention to their cause. It's one thing to write a letter, or even to celebrate Mass at the border, or to welcome the undocumented. It would be something qualitatively different if the bishop were to organize a strike in, for example, parochial schools or hospitals, and challenge his people to do the same. He would be saying that the Church is willing to pay a steep price to stand alongside the undocumented. He would also be challenging society to see a temporary inconvenience as a reason to rethink their values and policies.