Left-handedness has a long history of being considered inferior. Roman culture was superstitious, and left-handedness was associated with bad things. When Christianity became the dominant religion, some things stuck around among the culture. Up through the mid-twentieth century in the United State, some sociologists and psychologists theorized that left-handedness was associated with stubbornness and criminality. In fact, even today some cultures consider the left hand to be “dirty.”
It is most certainly true that the laity and clergy were people of their culture and therefore shared some of the superstitions of their day, including prejudices against left-handedness. However, there was never an actual Church teaching on the matter, nor was there a systematic program against left-handedness.