The controversy comes about because not all of the first group of bilinguals are included in what would be called the "elite" of society. Although most "elite" bilinguals are much better off than guest workers, the Romany in Europe, etc., they still have real concerns caused by their decision to live with two languages. And although they do not have the loss of culture at stake, the loss of language for the parent or parents who speaks the "outsider" language can indeed be a serious loss.
The theory, based on a suggestion by a linguist named Weinreich, held that bilinguals could be classified into coordinate bilinguals, who had a completely separate system of meaning and expression for each of their languages, and compound bilinguals, who had a single system in which one language was dominant. It was suggested that the pattern in which an individual had become bilingual would determine which group he belonged to. Many misunderstandings arose - with some people suggesting that compound bilinguals were confused or that bilinguals were always forced to translate in their heads. Experiments designed to test the theory, however, gave ambivalent results, and the design of the experiments themselves was questioned. Eventually the theory was discounted. Additional information can be found in both the Grosjean and the Harding and Riley book, listed on the Books and Newsletters page.