I agree that English should be the official language of the U.S. for purposes of legal transaction and interaction. Multi-lingual societies are not bad, but they impose costs that are unnecessary. This does not mean that we should not teach other languages in school, nor that we should be unaccomodating to those of different backgrounds, but for legal transactions, one language is preferable to many.
Currently, the United States has no "official" language. However, it is generally accepted that you need to speak English in order to fully function in society. This is not to say that other languages and cultures should be shunned; however, I think we waste a lot of time and effort trying to accommodate people who speak no English despite having lived in this country for years.
It can be argued that progress comes at the point where the sum of the parts together is greater than the individual parts counted individually. Such is true when a nation gains the collected knowledge and wisdom of immigrants from other lands. However, while it is always a good thing for people to retain their individual cultures, the true strength of a nation is derived from it's ability to come together as a common body to accomplish common goals. Lack of a common, singular language inhibits this joining together by requiring all ideas, instructions and directions to "jump the fence" linguistically with each translation. In a nation that already has difficulty communicating between regions of same language but different dialects, introducing multiple languages can only lead to greater misunderstandings.
Yes, I do think that English needs to be set as the official language of the US, and that all of the others need to be just secondary things that not all of the people need to know how to speak to understand everyone that is here it the nation.
No, English should not be established as the U.S. official language, because it would not make a substantial difference. It would, however, make people feel unwelcome. When translators are needed for official things, like court, interpreters are provided. There is nothing to be gained by making the official language English, because we already pretty much function that way.