We can at least try to understand our own motives, passions, and prejudices, so as to be conscious of what we are doing when we apeal to those of others. This is very difficult, because our own prejudice and emotional bias always seems to us so rational.
The most precious research to me came from the paperwork filed on behalf of my grandparents and great-grandfather. The ship's manifest showed that they could read and write. I am still emotional when I look at those boxes checked yes.