It is easy for us to write the good things about our relatives when writing a family history. It is much more difficult to write about the bad things and the mistakes that they made. It is appropriate to be very careful when writing about someone’s flaws so we don’t go too far and become distasteful to our readers.
I think that Dawn Thurston explains it best, “When writing family history, it’s difficult to create a realistic picture of people long gone. Genealogy data reveals little about how people looked, moved, or talked, or what strengths and weaknesses shaped their lives. Then there’s family pride. Absent any evidence to the contrary, we tend to idealize our forebears. We want them to be exemplary rather than human. I suspect the image that exists in our mind’s eye bears little resemblance to how they actually were.”
I think that we do our readers a disservice by only telling the good. A brief mention of the mistakes and bad qualities of our ancestors makes them more real. So, be brave and write the whole picture of your ancestors, then before you have it published have someone else read it over and make sure that you have handled it tastefully. You will be glad that you did.