The idea is that Latinos have a dual experience that whites don't have and that, all things being equal, they'll be able to pull from that experience and see things that whites don't. The problem with this reasoning is it implicitly accepts the logic (made for years by white racists) that there is something essential and unifying running through all white people, everywhere. But White--as we know it--is a word so big that, as a descriptor of experience, it almost doesn't exist.
Indeed, it's claims are preposterous. It seeks to lump the miner in Eastern Kentucky, the Upper West Side Jew, the yuppie in Seattle, the Irish Catholic in South Boston, the hipster in Brooklyn, the Cuban-American in Florida, or even the Mexican-American in California all together, and erase the richness of their experience, by marking the bag "White." This is a lie--and another example of how a frame invented (and for decades endorsed) by whites is, at the end of the day, bad for whites. White racism, in this country, was invented to erase the humanity and individuality of blacks. But for it to work it must, necessarily, erase the humanity of whites, too.
TNC of course makes the further (and necessary point) point that these are all fictions that become socially real.
P.S.: I realize the "negative dialectics" reference is probably too insidery for 98% of readers. It's a term that Theodor Adorno used for a title of his book. Hegel defined identity as "the identity of identity and nonidentity" - the idea being that any concept or act of identification glosses over differences and unifies things that are like in some ways but unlike in others. For Adorno, negative dialectics explores "the nonidentity of identity and nonidentity," i.e., disintegrating all of that.
Cf. the kind of weird quasi-discourse on whether Judge Sotomayor will or will not be the first "Hispanic" judge on the Supreme Court - the idea being that Justice Cardoza (whose ancestors, Portuguese Jews, emigrated to New York state in the eighteenth century) would qualify. If you try to pursue a purist/universalist idea of racial identity to the end, you start to focus on definitional descriptors (biological and/or cultural ancestry on the Iberian peninsula) that just wipe out all differences. "Hispanic" in this context may be as much of a lie-word -- that is to say, as powerful a concept -- as "white."