Here is that Robert Robb column from the Republic again. Again please note he's a conservative columnist who supports border enforcement, you will find that he thinks that so long as the "reasonable suspicion" arises in the course of ordinary police investigation of other crimes. That is what the law intends. However, he thinks the law doesn't provide adequate protection against what I would call "fishing expeditions," such as the ones Joe Arpaio has been engaging in.
Consider the following:
Case 1: An officer sees a car with a broken tail light. He stops the car, asks for a DL, notices that the people look Hispanic and don't speak English, and can't produce a license. The officer calls ICE.
Case 2: The officer sees a older-model car with a Spanish-language radio station bumper sticker. He notices the people look Hispanic. He THEN looks at the car closely for an onstensible violation and finds one, one that he would let pass if the people in the car looked like Anglos. He makes the stop, and if the DL is not produced, he calls ICE.
The trouble here is that, from the point of view of public record, these two stops are indistinguishable. The first officer is not fishing, but the second is.
Fishing expeditions are going to harm citizens and legal immigrants, because a group of people (and actually this could include Hispanic-looking people who aren't Hispanic at all, such as Bhutanese refugees). I consider that unacceptable.
Another set of cases I'm concerned about, which Robb doesn't talk about, are cases with pedestrians or passengers, not to mention cases where the police are called to a home but ordinarily ID is not required. If an officer comes to a home to tell them to turn their music down, he doesn't normally ask for a license. But if the music is in Spanish, and the people look like lower-class Hispanics, should he ask for papers? To me, that's fishing also.
Please notice that Robb makes a distinction between a disproportionate affect on Latinos, which he thinks is inevitable given any attempt to enforce immigration laws, and inividious enforcement, which he thinks the law either allows for or fails to effectively prevent.
One test of a law would be that if a law results in a group of law-abiding citizens being systematically treated differently by government and law enforcement as opposed to other groups of law-abiding citizens in virtue of the color of their skin, then something is wrong with the law. You should be able to go about your business, and if you obey the law, your should be treated just like everybody else.