A popular bumpersticker in the sixties and early seventies, it was aimed in opposition to the anti-war movement. The implication being that if you didn't agree with the U. S. presence in Vietnam, you didn't love America and thus should reside somewhere else.
Today, it is used primarily in ridicule of ignorance and intolerance.
More English Proverbs
More American Proverbs
16, POTD, Proverb of the Day,