Don't need to be a veteran to know that there is going to be lots of work to do on the border securing it. And I already answered your questions. That you didn't like the answer because it doesn't support your "theory" is not my problem.
Not really.
There are actually fairly few points that can be used to cross the border by more than a handful of people at a time. The vast majority of illegal immigration is not by "border hoppers", but by those who cross the border legally than overstay their visa.
And the system in place by the coyotes can only handle a low number of people at a time. Generally they drop them off in a remote area near the border, then they walk across to a prearranged pick-up point where they get into civilian vehicles for transport to another point.
A large mass of people? They will have to cross at a major border point, like Juarez. Where they can try to break through then immediately blend into a large urban area, like El Paso. If they try to break through at a place like Antelope Wells or Ojinaga, then they are pretty much in the middle of nowhere. And easily collected up on the US side.
One thing about the US-Mexico border, it is one of the most inhospitable on the planet. Even with illegal immigration as it is, it is estimated that as many as 500 die each year trying to cross. Mostly abandoned in the desert by their coyotes, with no food or water and 50-100 miles from any kind of habitation.
Myself, I mostly see this caravan as even more proof that Mexico has become a failed state. They are hemorrhaging people in ever increasing numbers to the US, over 10,000 a year are killed in their internal drug war, hundreds of politicians have been killed who oppose the drug cartels, and mass graves have been found of migrants who were used to transport drugs into the US then killed.
The very fact that they could not stop this massive flood of immigrants is yet more proof that they are failing their own people.
I know that when I lived on the border, most of the news I saw sickened me. Drug treatment hospitals in Juarez attacked, decapitated bodies hung from overpasses so common they were reported in morning traffic reports, dead bodies found in the desert were literally every day events. And with the cartels starting to move into human trafficking in addition to drugs, things are only getting worse.
Not that long ago, a female reporter in Mexico broke a story where an influential businessman in Mexico was involved in prostitution and child pornography. She only went public on the story when local police refused to get involved. Shortly after breaking the story, she was arrested in another state and brought to the state where the businessman lived in, the entire time the officers transporting her threatened to rape and kill her.
She was able to get out on bail, but another newspaper shortly afterwards revealed taped conversations between the businessman and the Governor where they conspired to have her kidnapped. And were planning on having her beaten and raped, possibly even killed if she did not agree to recant the story.
Of course the reporter (Lydia Cacho) tried to bring the Governor to court over this. But the Mexican Supreme Court determined that she had no case and dismissed her charges.
That is life in Mexico. And most of these migrants are from Guatemala and Honduras. Then people wonder why I consider most of Latin America to be a series of failed states.