Here's the difference
In the past, the "old country" was far away, today it isn't. Many Poles, Germans, Italians, or whatnot may have come over here, but their ties to the old country were lessened by the distance. The massive Mexican influx of today is different. The new old country is right next door. What happens when the SW is saturated with Mexican immigrants and they decide they'd be better off seceding from the US and joining with Mexico? The chance of this happening with the Swedes, Poles, Chinese or other groups was nil, but with the Mexicans it's an inevitability. Groups such as LARASA, Mecha and others are actively pushing for it. This is nothing but a recipe for disaster, a disaster caused by the political games of short sighted politicians.