I understand the backlash just in the sense that there is a fear that American identity and culture are eroding. America was always a melting pot: Newcomers learned English and became Americans. I think the ad reminds everyone that that has changed. Today, the United States is turning into what we would call in Canada a cultural mosaic. The melting pot and the mosaic each have their pros and cons, but as a Canadian who is somewhat disappointed in his country's lack of distinct culture, I understand why the ad stokes American fears.
Obviously there's some racism and xenophobia behind the backlash, but I think it's wrong to assume that every dissenter is some sort of racist.
Eh, that's the narrative from some quarters but it isn't the reality. Today's immigrants are indeed learning English (maybe not necessarily the older first-gen folks, but their kids for sure); and back in the day it was
quite common to have long-lasting non-English speaking enclaves. You know how the Pennsylvania "Dutch" still speak German? Yeah there was a
lot more of that in the 19th Century. It took a hit with WWI and the associated xenophobia, but immigrant communities continuing to speak their old tongues has been the norm for the vast vast majority of American history.