Tragedy of the commons. If 99 people will endlessly argue with you and 1 is rational, you'd just do a blanket ban on giving explanations. I've frequently found that you just need to get people started and their rant will probably not end. Has always been true on Internet. Has become truer in day to day life for me too. At a certain point, you just want to switch off the tap.
But do you actually have to argue back with those people? If I had to give a feedback to a candidate, I would just send the feedback, read their response (if I cared for it), and then set an email rule to autoforward all of their future emails to a separate folder that I have for stuff like that that I never open.
