Actually, the use of sinister to mean left stems from Latin. In Latin, the direction left was called "sinistra" and the direction right was called something along the lines of what we would hear as "righteous". People who were left handed were considered to be defective or deviant and more prone to criminal enterprise - hence the English adoption of the word 'sinister'. People who were right handed were considered to be better people, and thus we adopted the word "righteous".

Four years of advanced Latin didn't go to waste!

some of it's magic
some of it's tragic
but i had a good life all the way......
~jimmy buffett