Earlier quoted context omitted.
It kind of already is happening in the US right now in the form of "Family detention centers" intended to detain non-citizens slated for deportation. If Trump's administration seriously plans on "rounding up" millions of people for deportation, they'll have to be lodged somewhere while they are tried (assuming they're granted trials, who knows anymore) and travel arrangements are made. http://www.nytimes.com/2015/02/…
Strange how enforcing borders began to be seen as controversial. The explanation that makes the most sense to me is, some people see free movement across borders as a human right, while others view a country as their home, and so should have the right to decide who to let in.
Passport-based travel was introduced in most of Europe as a 'temporary' measure, for the purposes of fighting WW I.