If all immigrants are required to know and use English there wouldn't be as much discrimination. If we travel to another country, do we expect the local populace to speak English or the native language? I would expect the native language and we would travel with translation books, software, etc. in order to communicate. Shouldn't we expect the same thing in the US?
With a designation of English as the official language, federal, state and local governments and other business would no longer have to incur the costs of translating written materials.
This is a country of immigrants. The home languages should be preserved, but I am born in America and I shouldn't have to learn Spanish just because I live in the Southwest! And what about all of the other languages of this world?