"I've been thinking I might leave the party. A lot of my Latino Republican friends have been talking about it after this law," - Adam Bustos, a third-generation Mexican-American, who has voted Republican since Ronald Reagan ran for president.
The GOP is now doing to Latinos what it did to gays. Its leaders - by backing the Federal Marriage Amendment in the last decade and now the Arizona law in this - are essentially saying that they do not understand how these measures could impact a minority's collective psyche. Whatever the technical merits of either measure - and there were intellectually coherent (if, to my mind, unpersuasive) defenses of both - the lack of empathy or understanding is the real issue. It places the Republican "us" against the minority "them." This is not just a failure of empathy; it is failure of judgment. The votes of Latinos will be massively important in the very near future, and the number of people who know and love gay people grows daily.
The Republican base's inability to place itself in the shoes of homosexuals who are being told they could be second class citizens for ever or in the shoes of Latinos being told they are effectively guilty before being found innocent is a fatal moral and political gambit. Once your party has revealed that it cannot empathize and is willing to stigmatize an entire minority, it takes decades to reverse the damage.