Some of my favorite "wrong" or erroneous 'beliefs' (apart from the Flat Earth, and geo-centric beliefs)

-- Luminiferous ether: that light propagates via the "ether" medium -- "Bad air" theory of infectious diseases (which is still held in many countries) -- "Stress causes ulcers" -- Leprosy is contagious -- The belief that first five (or two, or three) years of a child's life determine his/her personality in adulthood. This is one is still widely held and accepted.

Oh, and just for kicks: 'Intelligent Design' and its variants. :-)

And just to throw it out: What will it take to convince that Global Warming / Climate Change is real? This is perhaps one of the leading least-understood / most controversial beliefs of our times.