Here is another problem, The Visa Waiver Program! We allow citizens of these 38 countries to come here for up to 90 contiguous days without a visa.
https://en.wikipedia.org/wiki/Visa_Waiver_Program
Notice though Mexico AND Canada, and most if not all of Central American countries are not on the list.
They still have to meet the requirements, they don’t just automatically hand out waivers to everyone from those countries. I know at the port near me when people enter from Mexico they have to show their documents at the border, and do the biometrics, and criminal check here and in Mexico or their country of citizenship is done. The exceptions are if they have a border crossing card, student visa, work permit, similar or they will have to prove their ties to their country- proof of home, job, business, things like that in order to cross. The major difference with the waiver is they don’t have to go to the embassy for an interview, or apply far ahead. Many are turned back for not having what they need or for other reasons.
Again we know NOTHING about those that cross the desert. Border Patrol here detains murderers, rapists,molesters, MS 13, people who were deported already, people from nearly every country in the world, including those that sponser terrorism- and much, much more. We really have to secure the border to secure our country.