Pew: Fewer Americans Believe U.S. Culture Is Superior to Others | TIME.com
It's a trope that's sometimes used to address certain issues, but it isn't applied uniformly. When there is renewed discussion over problems surrounding European multiculturalism, it's not as if American liberals still use the trope. Nevertheless, it's still somewhat present in discussion.
Personally, I think it's merely used as a means to promote policy change domestically.