In the US, the legal/illegal debate glosses over the fact that the US agriculture and hospitality industries have relied on illegal immigrants for cheap labor for decades. Apparently this includes Trump's golf courses and probably hotels.
Plenty of businesses have relied on immigrants entering legally or mostly illegally and working for low wages picking crops, cleaning rooms, etc.
So there has been a wink-wink system in place, a grey area, where everyone knows what is going on and ignores it. That's something that should be fixed so:
1) Mexican workers can legally enter on temp visas during the harvest season (nearly half the year if they follow the crop route north). These workers should be given a decent wage and have rights, something that there illegal status currently denies them.
2) Companies should only be able to hire legal visa holders so that they pay taxes and treat the workers fairly.
First figure out a system for the illegal workers that are wanted and needed and then worry about other immigrants.
Btw, the immigration system is horribly messed up. I don't know the current horrors, but late 80's NYC took a host of condemned or otherwise forfeited old hotels the city unintentionally owned and used them to house detained immigrants. Problem was these hotels were right in the heart of the city with multiple exits and windows, and it wouldn't have been hard for any enterprising detainee to slip out. So they started chaining folks to radiators and such to keep them locked up. Finally this was ruled by courts as unsafe in case of fire (and possibly inhumane).
When I acted as a lawyer for a non-profit, besides my scheduled meeting with a detainee, I was told to ask about 2 Somalis who had disappeared in the system. They were allegedly no longer at the JFK holding facility, but it was unclear where they were. They had persuaded an INS judge to order the guards to bring the 2 to the Manhattan immigration, but when they failed to be brought, the judge had no power to compel the guards to do so. I was supposed to ask the authorities mildly where these 2 guys were, and when they would be brought in. Also, I was supposed to ask any other Somalis I ran across in the facility who were being held at one of 3 detention centers if they knew of these guys whereabouts.
Detainees aren't officially in the US as they've never passed through immigration and legally entered. So their rights are very limited. They don't even have the right to a lawyer or due process, except as provided by treaty. The only reason we were allowed in was because one ex-lawyer for the organization became an immigration judge and arranged for it. But we had to tippy-toe around as they could cut off our access arbitrarily at any time. Hell, they could just disappear our clients.
The Somalis in the early 90's were actually lucky. They had a network and some influential Somalis were allowed in to the immigration facility to interview detainees and often arranged families for them to stay with while they were waiting for their cases to be adjudicated. I forget exactly, but the average case to something like 2 years to process. It was all very Mickey Mouse.
And that's not even to get into the political aspects. Back then refugees from Nicaragua had a shot at asylum because they were fleeing a commie gov't we didn't like. But anyone form El Salvador had close to a 0% chance because they were merely fleeing right wing death squads organized by a gov't we supported.
All of which is to say the fact that they separate small children from parents and don't keep track of where anyone went doesn't surprise me in the least. Maybe they'll find those 2 Somalis they lost track of back in 1991 ...