While I was not offended by it, I did feel that the ad was in bad taste. I do believe that America should be celebrated for its multiculturalism, and the freedoms afforded to all her citizens, but I would like to see those immigrating strive to be "more American" than complaining when America is not enough like the place from where they came (i.e., just because you don't eat beef where you come from, don't expect to make me/us stop eating it here). If you are fresh off the boat, I do not expect you to know American English, nor do I expect you to have mastered it within a given time; but I do expect you to strive to learn and adapt to it rather than claim that you are faced with some negative '-ism' when I have no desire to learn your language.
If I come to your house for a stay, I don't expect you to change all of your ways to adapt to my way of life; I must adapt to my new environment. Adapting != changing who you are as a person. While I do not think this ad intended to encourage Americans to blindly conform to and accept all those from different cultures while giving up pieces from your culture, I felt it came across that way in order to be PC.