Load of horseshit.
Mexicans are as Westerners as Canadians are. They read Shakespeare and Homer and Goethe, just as Americans (those who read) read Carlos Fuentes, Unamuno, Lorca and Cervantes. Hispanic culture, its art, music, literature are as important to Western civilization as the Anglo-Saxon or Germanic are.
There's no Western Civilization without Cervantes, Unamuno, Goya, Velazquez, Sorolla, Picasso, Dali, Kahlo.
There's also no America without Spain, no Texas, California, Nevada, Arizona, without Mexico. There's no Tex-Mex, no Tacos, no Ranches, no Cowboys (the entire institution was invented in Spain and exported to the Americas via Mexico).
Any claim that there's some BIG CULTURAL DIVIDE with Mexico is based on utter ignorance.
Also as an American living in Europe who extensively traveled and worked some in Mexico. There's a significantly larger cultural divide between any European country and the US than there is between the US and Mexico.