It is all too true that esp in the U.S., the main drive behind the movement to stop the SPP and the "North American Union" is based on Conservative fears about illegal Mexican immigrants (who Lou Dobbs believes all have leprosy!) and racism.
Even though some of the strongest opponents to deep integration are prominent Conservatives, I also fear that their involvement both discredits opposition to deep integration and puts the focus in the wrong place.
It's an issue Vive struggles with constantly, trying to decline or avoid partnering with the organizations who oppose SPP purely out of fear and hatred and a race-based view of what nationalism means.
Read this very popular blog entry for more thoughts about this.