In this excerpt from President Kennedy's 1963 Civil Rights Address, he included the examples of American troops in Vietnam and West Berlin for what purpose?

"Today, we are committed to a worldwide struggle to promote and protect the rights of all who wish to be free. And when Americans are sent to Vietnam or West Berlin, we do not ask for whites only. It ought to be possible, therefore, for American students of any color to attend any public institution they select without having to be backed up by troops."