My own view is :

1. Mass downvoting of most/all a user wrote regardless of content defeats the purpose of the karma/score system and therefore is harmful to the community.

2. Mass downvoting is rude and painful for the target, and therefore is harmful to the community.

So we should have an official policy forbidding it. For the current case, I would support using first 1. (it's always good to ask for reasons behind an act before taking coercive action), and then apply any of 2.an 4. and 5. depending on the answer (or lack of it).