When you factor in the minimum wage in US is around $7 and if you're a waiter or waitress (or any job where you can get paid tips (20% going rate in US) it could be as little as $2.20 ph) and the first part doesn't really factor in...bigger issue is no federal taxes being paid to support the few "state benefits" they receive. Crime is a different issue but much of that isn't "immigrant" driven although Mexican drug flow is definitely an issue down south. Go to Boston, Chicago, NYC or Phillidelphia and see how many Irish folk have overstayed their Visas and disappeared off the system.......I've got a Buddy in Boston who is a musician and reckons that more than 50% of bar-staff in that City are paid "off-books/cash-in-hand" (his wife owns a bar in Brookline and that's how she pays her staff. She was in the US for over twenty years, and illegal, before she first married the first time to get her Green card. There are lawyers who specialise in such things bizarrely). Trump is majoring on the Mexicans as they're an easy enough target and makes it "look" like he's tough on immigration, it's just rhetoric and vote gaining in the worst populist fashion.    

That's a fact but we're looking at almost a slave economy as they get paid, not always, below the going rate.  Is that a good thing, add in the crime that goes with it, IMO, it's not the solution.  A double edged sword I suppose. 

I spend a fair amount of time in Texas, Dallas mostly, and our friends out there reckon without the "illegals" and the "gig economy" it would be much more difficult to get the more menial tasks done and the more basic jobs filled.....a wee bit like the UK after Brexit.