I broke it down almost three years ago in my blog post, Federal Government will not be Maricopa County's Savior, one of the main points being that the federal government is just as bad if not worse in handling the immigration issue. I think of Arpaio as an extremist clown- he is a spectacle that pushes the limits of what the public will accept. He makes nearly everyone else who is pro-immigration enforcement (aside from Pearce who was right there with him) look responsible and reasonable. So the federal government militarizes the border, holds thousands of migrants in detention centers and/or deports them, still conducts huge raids (Obama's raids surpassed previous ones, i.e. here and here), etc,. but they get to decide, to the delight of many, that Arpaio just went to far because he's been using his federal authority to discriminate.
"The Department of Homeland Security is troubled by the Department of Justice's findings of discriminatory policing practices within the Maricopa County Sheriff's Office," Napolitano said in a statement. "Discrimination undermines law enforcement and erodes the public trust. DHS will not be a party to such practices. Accordingly, and effective immediately, DHS is terminating MCSO's 287(g) jail model agreement and is restricting the Maricopa County Sheriff's Office access to the Secure Communities program." (Source).
Apparently the federal government knows how not to erode the public trust. For similar reasons I have a problem with people focusing on the "innocent" victims of racial profiling and such. Sure, go after the real criminals, we won't question that concept, just as long as all the people caught up in the deportation/detention system are the ones you say you're going after- because blatant maliciousness and hypocrisy erode the public trust, the status quo doesn't.
Yes, I'd like to see Arpaio gone, just as I liked seeing Russell Pearce gone (it'd be better if he was goner) but the illusion of victory distracts from what's really happening. As I've mentioned numerous times, the Phoenix PD continues to deport more people than MCSO, but they do it without all the media hubbub, and therefore without comment from Stephen Lemons and migrant rights groups. Arpaio is the face that can be pasted to a piñata, but he's not the only one we should be hitting with the metaphorical (or not) stick.
Some of what I wrote in early 2009 is pretty out-dated, but the following concluding paragraphs are more timeless.
One problem with appealing to the government is that to do so would require not being a threat. But any real just solution to the “immigration problem”, inevitably involving the dismantling of NAFTA and other neoliberal projects, as well as a serious change in social/political structure, is and always will be a threat to the government.
Another problem is that the government has an interest in appearing to be able and willing to deliver justice. But overall it is not in its interest to truly liberate the people from injustice and in fact its existence is actually antithetical to such an action. It would like to have people ask instead of demand changes, however, and would like us to think of it as a benevolent force in such cases when it’s actually worth the time to make reforms that benefit the people. Therefore, if we ask and they give, they are the heroes. If we demand and they give, they are still the heroes although we still have some sense of having played a part.
Related, the government is not a just one. We cannot expect a government that has been built on racism and continues to practice it in various ways (much higher rates of incarceration of people of color than whites, lack of indigenous rights, wars, just to name some examples) to be a force against white supremacy. The operator of immigration detention centers (or the ones who outsource private detention facilities), the performer of raids, is not the one whose going to save us from the similar actions of the Sheriff. He is doing their work for them. He's just doing it in an extra "look how demeaning i can be to these people" way. If the federal government does anything about it, it will only be to legitimize and continue its own actions and those of other jurisdictions.