Honestly, before I say anything, I think that their should be something on this website keeping people from having their polls say things like "OMFG! ONE PERSON AT ONE TIME AT SOME PLACE SOMEWHERE DID SOMETHING HORRIBLE!!! Should something mildly related which may or may not be relevant which I disagree with be banned?
As for the question, yes. I believe an official language would be very beneficial to the United States. People shouldn't be forced into camps until they know English, but requiring that things be printed into one language would help deter misunderstanding amongst cultures while helping those who learn the language to get jobs and be more accepted into the society in which they live.
The official language of the US is English. If you are a person from a non-English speaking country coming to the US or any other English-speaking country, it's best you try and learn the language so you can talk to others, BUT that doesn't mean you can't stick speak in your native tongue to your friend and or family. But bear in mind some, Europeans have never been really good at assimilating into different cultures. I mean- look at South Africa. The majority of white South Africans speak Afrikaans (a derivative or the Dutch language) rather than the older more native languages of the land such as Zulu. But anyways there's nothing wrong with speaking Greek in the US and that woman who reprimanded that couple is wrong. It was none of her business and had no right to judge them.
I am appalled at the number of people who feel personally attacked when they hear others speaking a language they do not understand. It is in any visitor's or immigrant's best interest to know some English when they come to the United States, as any traveler would want to feel comfortable conversing in the common language. However, every person has the right to speak their native language with those who understand it. The United States prides itself on its freedoms. No person should be discriminated against for the language they speak.
Although I firmly believe immigrants should learn to speak English so that they can understand what is going on around them, there is absolutely no reason to insist that they speak English. This is a free country and people are free to speak whatever language they want. Anyone who comes to the U.S. will try to learn English but it is not easy for the older folks. We should be patient and tolerant with those who speak languages foreign to us.
I don't see any reason why a couple of people in private conversation cannot use whichever language they choose. If they are native to another country and more comfortable speaking to one another in their native language, then that is the language they should use. No one has to right to berate others for the way they choose to speak privately. There is no official language in this country.
If someone is simply visiting the United States and does not speak English, they should still be welcome to enjoy their visit to our country. Someone who lives here should learn as much English as possible to adjust to life here. However, people having a private conversation can speak whatever language they choose, and others should not be offended by it.