I'd appreciate an explanation of why criticism of unwarranted negative feedback justifies more negative feedback.

There's probably some law of diminishing returns, where commenting on something = (A1) utility, and commenting on how people comment on something = (A2) utility, and commenting on how people vote = (A3) utility, and you commenting on how people vote on you commenting on how people vote = (Z) utility, where it tends to go A1>A2>A3>...>Z, and probably Z is deep in the negatives.

You should also distinguish between types of feedback: receiving downvotes for an unknown reason may be frustrating to you, but it doesn't clutter up the threads. You complaining about every time you get downvoted does clutter up the threads. It's not the same type of "negative feedback".

In short: obsess less about karma.