However, the third one didn't strike me as so brutal, but I also agree that the beginning could have been worded better.
This reminds me of several discussions on how many people with some characteristics of aspergers/autism are bad communicators because they're worried about being right and not about the other people's feelings - and believe that saying what they consider to be the truth doesn't offend.
(I'm searching for some interesting articles on the subject, but I didn't save the links and now can't find them).
I have very bad communication skills myself, that's why I found Carnegie's points about other people's feelings so important (others might find it obvious).
Edit: I also think that most people in Hacker News are more inured to criticism, or able to take it better, and so might be harsher themselves - or not think it wrong when someone else is harsh like in your case.
Some commenters may say, well, we see the overall point and agree with it, those two details could be overlooked.
But, the whole point here about empathizing with the client, is that those are the two details that matter.
I could have structured this argument a little differently and been much more positive (a compliment sandwich, they call it) and lost none of the impact.