If I have some criticism to say, then I'll say it and probably won't vote the node down (as that would just be adding injury to insult). So I vote down a node when I don't have the eloquence or time to put my disapproval into words. So, no, I am almost never going to explain a down vote.

This has come up before several times. People have given lots of good reasons why they don't do what you are asking.

I'm sure there are occasions like you noted where an explanation is helpful. I'm also sure there are occasions where the explanation would just make you feel worse.

If I was trying to educate the poster, then I'd pick a method other than a down vote.

And if it is a single down vote, then just ignore it! It could be that someone got cut-off in traffic earlier or accidentally picked the wrong radio button. There are hundreds of voting monks here so one down vote means nearly nothing.

Actually, my advice when it comes to down votes is to ignore them all. You'll be happier and we'll be happier. If you look at the reps of all of your nodes, you probably already realize that rep has at least as much to do with quirks of Monastery as with the quality of the node, anyway.