Why was my comment on Explain down votes deleted? Why was the reply to it also deleted? And no others?
It was flagged as inappropriate by the community and the flag was deemed helpful since the comment didn't actually add anything constructive to the discussion. It was an out-of-context claim with no backing and was discouraging to a new user of the community. To put it more bluntly, it looked like a passerby using someone else's unrelated problem to go on a sidetracking rant:
Could be worse some one could be going through all your posts and down voting or un-upvoting them every day. Like someone here does. Ignore it.
And with the comment gone, the reply to it was superfluous.