Because gun sellers in the southwest (hell, most places really) take no responsibility for a straw purchase. Little old lady comes in, purchases 20 AR-15s, which are then reported stolen. Clearly a job for the cops not the gunsmith- but when that same old lady comes in a week later and buys 20 more rifles, well, she must just like hunting! From the gunsmith's point of view, he's conducting a legal transaction, so why should he care?
Hmm, well I think that could be solved pretty easily, anyone buying 20 rifles in a month without a FFL (Dealer's license) should set off a red flag for the federal folks doing the mandatory background checks. In fact it's pretty easily fixed, considering there is already a one handgun a month rule in Virginia, which is damn liberal with the gun laws.
That's neither here nor there tho, because people can always get guns, the REAL problem is border control. There is NONE. CBP thinks Mexico should police their half of the crossing, buuuuuut.. anyone who's been to the San Ysidro station can tell you, coming IN to the US is like going through an airport checkpoint, a nice reaming; but LEAVING this US- there is NO guard on duty, the Federales don't give a shit. Its literally a giant metal revolving door in the fence, with a big colorful sign that says MEXICO above it. If I wanted to smuggle guns in I'd only be limited by how many I could carry.
Yeah we've never really had a border. From a force protection standpoint there are better ways to deal with difficult neighbors than a wall. But you are right. 'cause of Mexico is a piss poor excuse to curtail
our civil liberties or start paying the Danegeld. Not like we don't do that enough already without their help.