One thing you have to realize about Hacker News is that people can accumulate pretty good karma points for postings that have a definitive/authoritative tone blended with some truisms. Not to bludgeon the equine or anything, but I think people find them comforting.
I don't think his comment in any way contradicts your post. I thought it added to it; his point is that not only are good protocols hard in practice (which you covered), they are theoretically hard (which you did not cover, hence adding to your point).