I can understand A being overly defensive as that's human nature and sometimes my first response to valid criticism is denial: "I can't accept this criticism because it makes me feel like a bad/stupid/evil person and I'm not". But it's possible to handle things badly with wounded denial and still not do permanent damage. I suspect it's the difference between rejecting criticism and retaliating against the critics. So despite having reacted with denial, I still don't get when someone doubles down on the offense and attacks with bridge burning vitriol. It creates the impression their initial offense comes from a position of insulated yet angry superiority, rather than human fallibility - edited to add "creates the impression" is wrong, it's "reveals the actual problem is", and "confirms the offense was informed by ideas of power".