The key phrase for me is this one:
bluntly letting people know when they are wrong, as if this will somehow endear others to them.
This sounds like it's definitely about signaling that you are right. The second sentence, though I do agree with it, doesn't seem like it's the main point of the paragraph because of the "also."
Like I said, you're reading that very differently to the way I read it. To me, it's about people not sugar-coating the truth, and not being diplomatic about the fact when they are right. In other words, it's all well and good knowing that, say, homeopathy is nonsense, but you don't get anywhere by insulting homeopaths (although it can be fun..)
On Quora: What are some stupid things smart people do? Examples of common types of stupidity that are typical of otherwise very smart people.
Lee Semel's answer in particular would make a great post here: a "to don't" list. You may wish to go through and identify the cognitive bias or biases each is an example of.