Why do some americans get annoyed when people speak something other than english in public?

You know what, thats messed up. You should be able to speak whatever you want it doesnt matter to me. And in my city in florida they're going to start teaching spanish as second language to kids and guess what every had to say about it????? "This is American we speak English here, they should learn English only, half the people here can't speak english right.." blah blah