Most people feel blunt, and "brutally" honest people are just stating the facts with zero empathy, compassion, or emotion, and since most people aren't emotionless sociopaths it strikes them the wrong way.
I think it comes down to this. A self-description of "being blunt" or "honest" isn't a free pass to be a complete twat. Honesty doesn't have to be accompanied by rudeness, bile or excessive judging.