First, by recent reports the recent downturn in the economy, particularly the construction sector, has already lowered the numbers of Mexicans and South Americans coming into the country. A few observers report some heading back south. Makes some sense. If they come for jobs and economic prosperity and they can't find jobs or easy money the reason to come, and stay, are diminished.

Second, much of the SW of the USA was Mexico less than 200 years ago. Two centuries is an insignificant amount of time compared to the history of the Mexican culture. Payback is a ... Not that I think they are really going to take over. At one time NYC was mostly Italian and look at it now. Things change. Get over it.

Third, drugs finance and fuel all the major criminal organizations. The Mafia was a small and poorly funded organization primarily concerned with protecting their ethnic group. While everyone knows about the Italian Mafia, ethnic Jews, Irish, Armenians all had organizations whose original purpose was to provide protection and organization for their communities.

All of them dabbled in the protection business, prostitution, gambling and other illicit activities as the need to serve an immigrant population declined but it was prohibition that allowed them the resources to grow and break out of their narrow ethnic and socioeconomic base. With the increased wealth and power also came the move into police and political system in a major way.

It is possible that if deprived of money from drugs gangs could get into kidnapping and other crimes but the nature of such crimes changes the dynamics. Dealing drugs and prostitution are widely viewed as victimless. Or nasty things people do to get by or cope. Kidnapping is not viewed as victimless or 'just one of those things'.