Epiphany - being multilingual is un-American?

This just hit me tonight – during an argument in the classroom, when I was trying to explain the benefits of not speaking English at home when a child is trying to learn English at school, it was implied that continuing to speak in one’s mother tongue is completely wrong. It took me a few nights to think it through, but I think what the message was, was that they thought it was UN-American. Teachers were saying how wrong I was and that people are practically obligated to give up their first language when they come here, and that they expect it. Do you think this is how people perceive being bilingual in America?? As un-American?