Historically, left-handedness was associated with evil, abnormality, pathology. Children were subjected to "re-education" (and to a lesser extent still are). The International Lefthanders Day aims at raising awareness for the left-handers' need to adapt a right-handed world to work for left-handers. Left-handedness is not a new phenomenon, the oldest evidence for the coexistence of both right- and left-handed individuals is from the Pleistocene (ca. 425.000 to 180.000 years before present). Homo neanderthalensis individuals, in fact, were right- or left-handed.
Faurle, C. & Raymond, M. (2004) Handedness frequency over more than ten thousand years. Proceedings of the Royal Society, 271, 43-45. Hand tree via