American adventurers and semi-official expeditions into Spanish territory were always a problem for them and they were understandably concerned.
The activity of the US Army in controlling illegals has never been much. Indians, Mexican bandits etc. were almost its entire concern.
I have never lived along the border but am very familiar with Illegals since I have lived in Chicago for 40+ years. We have LOTS of Illegals here. More than almost any other city.
I have heard there are large numbers of illegals in Chicago, are they from all over the world or mostly from Mexico and other Latin American countries?
I have no idea what impact illegals have on cities other than cities in the Southwest. I do know the border problems are not just people crossing illegally. There is an organized crime network on the border that is involved with smuggling people as well as drugs and almost anything else you can imagine. There is associated violence, other crimes, bribery, and corruption on both sides of the border.
That is why my priority has always been border security. If the border was secure, then I think there would be more support for a plan to deal with the illegals already here. It is complicated and won't be solved overnight, but without the border secure- it won't be solved at all. Even if a guest worker plan is implemented there will be people who do not qualify or do not apply that will have to be deported if the plan is to succeed. Without securing the border those deported will return in hours or days as they do now.
I don't see how any plan to deal with illegals can work unless the border is secured first.