Carlos presented these thoughts in a comment, but they are so good I decided to make them a full-fledged article in Saber Point. His quote in the blue field below is worth quoting again and again.
Though Hispanic myself--even if not a Mexican-American, rather a Cuban-America, which tends to come with a completely different worldview--I must say the whole Cinco de Mayo thing peeves me somewhat. Some of that irritation has to do with the somewhat ersatz nature of the holiday, which, I am sure you know, is not a big one in Mexico proper, at least outside the town of Puebla, which, my Mexican-from-Mexico acquaintances tell me, does go whole-hog in celebrating it.
All right, I admit my cavils at the lack of historical perspective are sheer petulance on my part. What does bother me much more is that Cinco de Mayo has increasingly become a celebration of Mexican-racialist irredentism--the whole La Raza-Aztlan thing--instead of the feel-good, healthy-ethnic-pride holiday that I remember Mexican-Americans celebrating in my youth. The change in perspective has not been good for the health of the American body politic; ethnics should, when in the public forum, not displace American traditions and symbols with those of their ancestral homelands. That is not just bad manners, if unchecked it can lead to the eventual balkanization of the society.
Face it: what is most valuable about American culture has been inherited from Anglo-Saxon civilization, going back at least as far as the common law and equity courts of Henry II. The real genius of the American melting pot was to turn all immigrants and their descendants, whatever their ethnic provenance, into civic Anglo-Saxons, with all that implies in terms of respect for the rule of law, the probity of elections, respect for individual rights, etc. Thus, men with last names as diverse and un-Anglo-Saxon as LaGuardia, Eisenhower, Kennedy, Cardozo, Nixon, Dukakis, and, yes, even Schwarzenegger (I know--I was disappointed in him too!) could become important American political and juridical figures, in the Anglo-Saxon civilizational mold.