I always celebrate on the 23rd of April as it's my Birthday.
I See nothing wrong with the people of a nation celebrating that nation's existence.
(Though if I were to wrap myself in the flag it would be the Northumbrian one)
St George is patron Saint of England because he intervened on the Norman side in a couple of battles during the Crusades.
This must be true because the then Pope says it happened.
Humanism is neither a religion nor particularly practiced in England.
If you'd like to celebrate anything else that day,it's the Birthday of Roy Orbison & ,er, Shirley Temple as well as Shakespeare.