Powerful letter! I can't see how an elder could read a letter like this and not begin questioning in their own mind whether or not they're in the troof.
The initial thing that I was concerned with was a feeling that I was being intellectually dishonest. For example, my universe-outlook required me to have a very critical view of many areas of science. Any time science seemed to contradict my set of beliefs (as in the raft of evidence against any global deluge ever occurring), I was to view it with extreme skepticism, if not outright scorn. This troubled my conscience for two reasons: First, I felt that if I were to hold that same standard of critical thinking to my own beliefs, they would be utterly obliterated. Second, I knew that many of the theories and facts I was being asked to dismiss were not only totally reasonable, but they gave every impression of being absolutely in line with the available facts.
Excellent line of reasoning, I had never thought of it this way.
I also felt like I had to write a letter to disassociate myself, sometimes I regret it but mostly I feel like I had to make a clean break from them, to satisfy my own conscience.