One could reasonably argue that the poison pen letters that Miss Strangeworth writes are not just nasty and mean-spirited, but downright evil in that they are designed to sow suspicion and set people at each other's throats.
Though Miss Strangeworth claims to be concerned with protecting the moral climate of the town, in actual fact, she constitutes its biggest threat. Far from encouraging people to live together in harmony, she actively seeks to create division, dissension, and mutual suspicion. By most people's standards, this would be regarded as evil.
A prime example of Miss Strangeworth's evil comes in the letter she writes to Mrs. Harper. In this poison-tipped epistle, she intimates that Mr. Harper is having an affair and that all of Mrs. Harper's friends are laughing at her behind her back.
If Miss Strangeworth really were concerned with the moral climate of the town, then she wouldn't write such letters. There's nothing remotely good about attacking someone who's on the wrong end of adultery. After all, Mrs. Harper hasn't done anything wrong here, so why should she be the one to be insulted in this way?
Here, as elsewhere, Miss Strangeworth's behavior is completely gratuitous. There's simply no need for her to write such an appalling letter. Far from improving the general moral climate of the town, far from doing good, her letter can only generate greater evil by making a bad situation much worse.