Because the author is a “stick it in their eye” bigot.
“Latinos love la habla not just because it’s part of their culture, but because we know what conservatives refuse to accept: Spanish, not English, is the most all-American language of them all.”
“Now, with an increasingly diverse America, speaking Spanish is just going back to our roots — roots that modern-day Know-Nothings fear being left out of.”
That statement from the author has to be one of the most ignorant things I've heard regarding English. One of the reasons English has become the de facto universal language (e.g. in IT) is its ability to absorb words from other languages in an almost Borg-like manner.
Another attempt at reconquista?
Making English the official public language makes it equally easy for all legal foreign immigrants. They can count on being able to converse at any public function.
These so called liberals ought to be tutoring people in English. But that would reduce the demand for public accommodation in Spanish. Offering alternatives to English is a nicety, and there is no problem making it common as English is in China. But one is jolly sure to see Chinese in everything there too — as is logical for that country. Why isn’t it enough to see Spanish treated in the USA like English is in China? As a voluntary convenience?