As President Obama made clear last month, some proponents of the Arizona law have distorted the truth to spread fear about undocumented immigrants. Governor Jan Brewer, for example, claimed that beheaded bodies had been discovered in the Arizona desert, but could not prove or even comment on her assertion. Such irresponsible claims have helped spread unfounded fears about illegal immigrants, intensifying the tenor of an already fraught debate. According to the Progress Report, some anti-immigrant extremists have organized militias, manned by combat veterans and neo-Nazis, to patrol the US-Mexico border. But potentially violent hostility is not directed only at undocumented immigrants: some opponents of the Arizona law have been targeted as well. Judge Susan Bolton, who recently blocked some of the law’s most odious provisions from taking effect, has received hundreds of threats from anti-immigrant extremists.

Tension in the state over the new law and Judge Bolton’s injunction against some of its provisions did not stop Sheriff Joe Arpaio of Pheonix from taking matters into his own hands

Arpaio has said frequently that he doesn’t need the law, which created a misdemeanor offense in Arizona for immigrants who fail to carry registration documents, and his track record backs him up.

Thursday’s operation would mark the 17th time Arpaio has deployed hundreds of deputies and volunteer posse members in an area of the Valley to root out illegal immigrants. Deputies typically take a "zero tolerance" approach to traffic offenses and then check the criminal history of the motorists. Some of Arpaio’s deputies who were trained to enforce federal immigration law used to be able to conduct roadside immigration screenings, but the office of Immigration and Customs Enforcement stripped deputies of that authority last year, forcing sheriff’s deputies to wait until they bring suspects to jail to determine immigration status.

This kind of quasi-vigilante policing is not an effective way to deal with our broken immigration system, or to dilute the threat of vicious anti-immigrant extremism. Indeed, Sheriff Arpaio’s methods merely contribute to the toxic atmosphere that makes an honest national conversation about immigration so difficult.