For many hundreds of years left-handed people were treated with suspicion and disapproval. This probably originates with folklore associating the Devil with the left hand in various ways. He is portrayed as being left-handed and was thought to baptise followers with his left hand.
Left-handedness as a curse may also be associated with the Latin word for left, 'sinestre', from which came the English word 'sinister'.
There are also unfavourable references in the Bible including:
“Then shall the King say unto them on his right hand, 'Come, ye blessed of my Father, inherit the kingdom prepared for you from the foundation of the world'... Then shall he say also unto them on the left hand, 'Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels'." (Matthew 25:31-34, 41)