It's not always that "natural" of a selection. Many native Americans were basically kidnapped and forced to learn English. Governments in the past have intentionally tried to eradicate languages with the mistaken belief that one language is superior and more communicative and another is barbaric or degenerative. This still happens in the form of dialect prejudice, which is institutionalized in the American public school system. People tend to project their prejudice towards a particular group of people onto their language. This has been proven many times with dialect perception experiments. I think we have an obligation to preserve cultures and languages that have been eradicated due to ignorance and prejudice, and we need to learn from the past and stop trying to enforce linguistic standards in school. If a single homogenous language is necessary, it should emerge naturally.

Having said that, languages do die naturally for socioeconomic reasons too, and I agree that it's unnecessary, and probably harmful to try to force people to use a language that they have no socioeconomic incentive to use.