The underlying contention is that it does not make life easier for everyone. Specifically, that the lack of cohesive American identity actually makes it harder for the people who matter most in the United State of America: Americans.
How does providing government paperwork in Spanish or Korean make life harder for an English-speaking American? And the contention that Americans only speak English is just wrong. Most do, but there are massive numbers of residents and citizens who have something else as a primary/first language.
What ever happened to being a melting pot. And taking on the poor, huddled masses? Growing up in Virginia, we were always taught our variety was one of biggest strengths, not a weakness.