The idea is pure bunk.
You make the 19 year old college freshman error of thinking Mexico, Canada and who knows who else WANTS to be part of the USA. They don’t. They want the opportunity, money and freedom we have here, but they want their own country.
Look at Puerto Rico as a prime example of this. If we wanted to, we could just take them over, but we leave it up to them. It is highly illustrative to see how they, as a small island, have handled it. They want all the benefit but none of the responsibilities.