Maybe I'm just being overly pedantic about a simplified anecdote, but that's the moment that you decided some issues couldn't be discussed with him? That seems like a fairly innocuous response. Couldn't you have pushed back, rather than assuming that the issue was entirely unresolvable?
The debate ran for about 3 months. He refused to acknowledge the validity of style guides and grammar. I tried, but he was resolute that because _he_ likes semicolons, other people could easily read his long and rambling sentences.
No assumptions involved, except the one that RMS wanted people to be able to read and comprehend his writing. I'm not sure that he did though.