If the US wants a border then the US taxpayers should pay for it. This is 21st century, a 10 ft physical wall won't stop a goddam thing you idiots.
You can't wall off the World, and why would you want to?
To your point. Nearly all those illegal immigrants came here legally and overstayed their visas. A wall would cost a lot, look bad, make us look bad in the eyes of the world, wreck the view for all those U.S. ranchers near the border, and be only minimally more effective, if that, compared to the present means of border patrol. Many countries come down very hard on employers of illegals making it it risky to employ them. Not the U.S. however. In the U.S., if an employer gets caught, which seems somewhat rare, there is a fine and a slap on the wrist. Ask Howard Industries in Ellisville Mississippi, how effective the fine is. They are the world's largest transformer manufacturer (I think) and have been caught twice already. Isn't it true that the Republicans have been the primary stumbling block to instituting effective control via employers?
The Obama administration greatly stepped up deportations, I imagine the Republican, Chicken Processors are going to howl about that!
On the other hand, we don't really need Mexico to pay for Trumps wall that's amazingly got 10 feet higher before it is even built.. (But why stop there, why not just announce that it is already 50 feet higher. Oh, OK. I get it. Trump doesn't want to seem unreasonable

. If we just got Trump's company to build the wall, the cost would be limited to the cost of hiring a few lawyers, because Trump would just lie and tweet that his contractors "did a bad job", and then refuse to pay them. He has proven to be an expert at weaseling his way out of financial obligations. Why not use his "talents"?