My understanding is a bunch of the low level boots on the ground Border Patrol people do appreciate the help, but the higher ranking ones officially deny it and can use their authority to swap people around to the point your friendly Border Patrol guy will get a surprise transfer then a bunch of assholes show up to your camp and wreck everything.

Another thing which trumps a lot of official BS is public consent and the interests of crime victims, that's how the anti-cartel militias in southern Mexico are doing it. Large public meetings with members of the public who make it clear they have popular consent and support. The landowners in bed with the cartels then just get rolled up and run out of town. Kind of harsh on their property rights, but the townspeople were having a lot to say in public statements and video about daughters being kidnapped and workers forced to work without pay.