Can you recommend any writings on how not to be blunt and mean? (I've been told I have a violent communication style.)

How To Win Friends and Influence People by Dale Carnegie is a classic work about social skills in general, and includes advice on this subject.

One tip from it: no criticism. Ever. Always word things in terms of positive alternatives: for example, instead of "I didn't read this post because it wasn't clear why I should" an option is "If you make it clearer what this post offers, more people will read it."

Instead of negative reinforcement- "you're bad, but here's how to fix it"- it's promising positive reinforcement- "this is how you get better." The implication of low quality is still there and some people will still get offended by it, but it's a step up from declaring low quality outright.