They have reasonable suspicion that there are illegals sneaking in using those routes.
I have no problem with them looking for criminals in this manner. The 4th amendment argument is irrelevent here, because there ARE large numbers of criminals going down that road.
Classic leftist argument. Lets allow thousands of criminals to pass freely just so we don't offend anyone on 'constitutional' grounds. Lets ignore the real-world to focus on political correctness so that a bunch of college-liberals can feel good about themselves and get famous on the internet.
Shit like this is an indication that this country is on the decline.