Widely Believed Fact 

An oxymoron that described a piece of information, theory or idea that despite being repeated frequently, quoted in the media, and known to practically everyone you ask in the street, is still false or misleading. Often used to describe theories in popular science that may have little or no valid evidence to back them up ( A fact that has not been proved is like a virgin who has intercourse, so the phrase is contradictory.)

From the quote by Professor Hubert Farnsworth ( Character in Futurama ) describing an old wives tale

Immunizations cause autism - It's a widely believed fact!

Widely Believed Fact by D F Stuckey October 31, 2008