Comment by anovikov

It is in the interest of the person to identify themselves and provide proof that they are a citizen. Otherwise they are held until their nationality is identified for deportation. Need large scale facilities where unlimited number of such persons can be indefinitely, and profitably, held, so they are had to do work of some sort (patching roads for example, doing earthworks, etc.).

People become bums because they can. There has to be no practical way to remain a bum.