The American Civil Liberties Union is directly collaborating with the Mexican government, possibly to sue the U.S. government in furtherance of illegal activity. The Mexican government has a great deal of political power inside the U.S. and they use it to push their money-making agenda: sending people north to the U.S. in order to receive billions of dollars. Those billions help prop up their corrupt government and by sending people north they also get rid of those who might press for political reforms.
The ACLU is on the Mexican government's side, not on yours.
Now, of course, some of the things the ACLU does are commendable. However, their bad, illegal activity-enabling activities aren't on that short list. Needless to say, the media presents them as a mainstream organization and allows them to hide behind their anodyne name. The ACLU is very selective in which cases they choose to pursue. When it comes to immigration, almost every single case they've been involved in would further illegal immigration and assist those who profit from illegal activity such as the Mexican government and corrupt businesses.
One of the best ways to do something about them is to go to a public appearance by one of their representatives and ask these questions on video.