Why would the Border Patrol hire someone with dual citizenship?(especially MEXICO)?

I guess it's beyond Mr. Gonzalez's understanding that maybe his beliefs present a conflict of interest. He should have been fired, or at least removed to a position that wouldn't have him in contact with people who may be crossing the border. I'm sure no one would disagree that if a Muslim sympathized with the fanatics who wish to destroy the U.S., he shouldn't be allowed to patrol the border; so why should Gonzalez?