Humorists or people who are frequently making jokes will tell you that once in a while they say something without considering its impact; then they wish it undone. Emma's comment to Miss Bates at the Box Hill picnic is a good example of that in JA's novels. I think of the tasteless comment in this letter as another example.

I know that evidence was provided yesterday in a few posts leading us to conclude that Cassandra Austen did not destroy any of her sisters' letters. Before this evidence, it was comments like the one in this letter that lead me to believe that her sister could have done it. Who wants unkind thoughts of a beloved sister (or Aunt) preserved for generations to see? Two hundred years after the author's death you feel deprived, but I completely understand her family's feelings, and would expect my family to do the same for me. In fact, if I became famous today, I'd start shredding tonight.