Sounds like the original post he was replying to was a hatchet job to begin with. The author did an admirable job of not getting down in the mud, I'm sure it was difficult not to take the original post personally and respond in kind.
Because, as I'm reading the response, the original post had a number of inaccuracies and FUD that it's not a good idea to leave out there unanswered since people will then assume they are true.
Yep, that was the main motivation. I should've made it clearer (I hope some edits to the post helped). It's far from the first post like this but I noticed some of the factual misconceptions seem to be picking up, so I wanted to set them straight on the record. But I didn't consider the tone enough, and I regret this. I hope it's a little better now. :-)