Miami survives just fine with mostly Spanish speaking. You can go days without hearing English anywhere plus it may do Americans some good to learn a second language good for brain.
I don't doubt that it might be good for the locals to learn another language. I do however find it more close minded that the foreigner does not adapt to the locals.
I have lived in Miami and I find it pretty crazy that someone who was born here cannot get help at Walgreens because an immigrant does not want to learn the local language.