There are many myths that get repeated so often that people aren't even allowed to challenge them. How many times have you heard it said that employers posted "Irish need not apply" signs in the late 1800s? Nobody has even been able to find any of those signs or a photograph of them. Or that Herbert Hoover's government did nothing in 1930-32 to try to thwart the depression. Or that FDR's administration ended the depression. Or that the stock crash of 1929 "caused" the depression.
All of these myths are designed for a purpose.