The potential damage that one person can now cause online is real and substantial. All it takes is one malicious individual to rile up the online troops to doxx, smear, and ruin a person and their career. And there's almost no risk involved in participating in such an act -- you are anonymous and not held accountable for anything you do.
So while Kathleen's response might seem a bit excessive, I can certainly understand why she acted that way. She was being attacked by an individual who had all the voice and reach in the world, on a mission to destroy her literary work, using a platform that's frustratingly conducive to mob-creation but not debate. I might have done the same.
I don't know what the solution is, or even if one exists, but this is a real problem. We saw the other week how Twitter was used to volley targeted death threats, and how the individual on the receiving end felt genuinely unsafe for her life. And yet Twitter, Reddit, et al. are very blasé about the severity of it all. You wouldn't want to hurt your growth rate, I guess.