I also heartily recommend that book: it is fantastic.
But in regards to “negative comments” one challenge is what to do when faced with a situation where you sincerely believe something is harmful if not strongly countered?
For example yesterday on HN there was a post about online dating, and a number of comments espoused an idea I viscerally believe is actively harmful: that you should strive for some idea of “good communication skills” that facilitate reading strangers’ body language in public and determining how to make an advance for dating.
Now, I really believe this is harmful advice: it leads to actually hurting people in the form of perpetuating social norms that bother people in public and put them in unwanted, uncomfortable positions, and cause impressionable readers to believe this is not just OK, but even healthy.
In a case like this, I am still at a loss of how to apply the sincere listening and positivity approaches of How To Win Friends... because there’s an overriding moral implication that the statements have to be visibly refuted and challenged, not to “win an argument” not to persuade the original author, but to leave a visible marker for impressionable readers about the serious danger embedded in what’s written, to spell it out clearly and not leave it to chance interpretations.