We tend to label them as Good or Evil as a way to distance ourselves from our potential of becoming one or the other. If Gandhi is a god, then we don't need to hold ourselves to the same standard as he did for himself. If Hitler is Evil, then we can rest assured in knowing that we will never duplicate that Evil.
Gandhi was a man of many faults. Hitler was a man of many good qualities. Gandhi's faults do not outweigh his good and Hitler's qualities do not outweigh his evil. But they are reminders of the humanity of these men. They were both complex beings and their roles in human history should not be diminished by oversimplifying those complexities.
More relevant is that we must understand that we have the capacity for good or evil that these men possessed. We may not have the opportunity to act on our good or evil impulses at this point, but they are there. So we must use every moment to better ourselves while recognizing our capacity for evil lies just under the surface.