TL;DR
I like the second proposal.
Anonymous downvoting should be a privilege earned at a much higher
rep. I'm thinking 1,250 or 2,500.
Pertinent considerations
• The privilege of downvoting an answer (125 rep points) is awarded after earning the privilege of upvoting an answer (50 rep points). The community trusts the user to cast downvotes, at his/her discretion, responsibly.
• The majority of users are disgruntled at receiving an unexplained downvote.
• Anyone would feel confused by two downvotes in a row, with no explanation, if they had spent time writing a post to the best of their abilities.
• If there is a comment helping users see where the problem lies, they can edit and improve their answer/question.
• Likewise when questions are put on hold it is accompanied by an explanatory note, which indicates what the problem might be.
• Some users do not care or never ‘listen’ to comments. That is their prerogative. And downvotes are like water off a duck's back to them.
• Some users will nitpick continually. The commenter or answerer may read abusive comments. There are users who thrive on being confrontational, it can be exhausting (and a waste of time) arguing with them.
More often than not, when I explain to a bemused poster the motivation behind any downvote, the OP will edit their post; the stumbling block is removed, and I delete my comment, and/or reverse my downvote. I'm not always right, and sometimes an answer gets upvoted despite my observation/objection/criticism. And that's fine, at least I have voiced my downvote, the user knows why and can disagree with me. And that's perfectly fine. I may or may not change my own mind. But other users can see my comment, and make their own decisions.
Medica in her meta post: How to guarantee getting downvotes without explanation, listed three possible reactions from users who receive motivated downvotes: 1) Moaning and whining. 2) Immediate launching of personal attacks and insults. 3) Revenge downvoting.
If all downvotes had to be explained, some people might be less
inclined to downvote. (Raise your hand if you've ever explained your
downvote only to get sucked into a bitter and hostile debate.)
J.R.
I struggle to remember the last time any of these incidents happened to me because I left a comment attempting to explain a downvote. On the contrary, it's been my experience that many users have responded thoughtfully, and were appreciative that somebody took the time to comment as to why their post may be misleading or inaccurate. (*Raise your hand if that has never happened to you.*) But I have had [short] heated debates with users, unrelated to downvotes. Insults; disagreements; accusations; teasings; rudeness; and sarcastic replies etc. occur, regardless of downvotes.
[A brief note on sarcastic comments on EL&U: how can a user tell if it is said with a smile; a wink; a smirk; or with a snarl? IMO they can be thinly-veiled attacks.]
Tip: If you cannot handle the occasional, mild online abuse, don't post opinionated comments or answers in the first place.
Proposals
The OP—who has forwarded two proposals—does not say he wants every downvote to be explained. The first proposal asks that the first downvote includes a motivated comment. Subsequent downvotes do not require a comment. If the comment left at the first downvote is accurate and fair, my supposition is that the incriminated post might attract further downvotes because subsequent downvoters will agree with the commenter.
The second proposal argues that the user must earn the privilege of anonymity. I'm in favour of the second proposal.
Let's consider the instance when a question is put on hold, the OP still has the opportunity to edit his post.
A question is only put on hold not closed outright, in order that it
can be reworked and re-opened [brought off-hold].
Andrew Leach
There's also the help centre which provides tips, and guidance on how to keep questions on topic. If you can have that for questions, what's wrong with leaving a comment beneath poor answers?
But sometimes a downvote says all that is necessary, just as an upvote may do.
TimLymington
Sometimes that is true. Not all posts need a motivated downvote, especially if the user is unregistered and has written utter drivel.
But sometimes:
an answer will basically consist of one word, with no references or support.
people post good answers to questions which they think the OP should have asked.
a biased, or loaded, or strongly opinionated answer/question will be posted.
a correct answer, which was obvious to any native speaker, will be posted; but without any explanation.
answers will have not have addressed all the issues.
correct answers, written by non-native speakers, will contain significant grammar, spelling or punctuation errors.
answers or questions are formatted so poorly, they are unreadable.
the poster has not fully understood the question.
In all these cases, and in many others, a user may be justified in casting a downvote, but to the OP, the reason for the anonymous downvote may not be obvious. Why can't one comment be left explaining one of the reason(s)? Helping posters improve their answers or questions actually benefits the site. It's "pro-active", it's "constructive", and a civil exchange of ideas can lead to one to reconsider their answer or downvote.
And yet after two years of participating on EL&U I still don't get why there is always such a strong opposition to encourage this sort of behaviour.
"No!" everyone will cry in unison, we all want this to be the standard behaviour on EL&U. If that's the case, how do we encourage this behaviour? How do we cultivate a civil and fruitful exchange of opinions?
Perhaps if the privilege of anonymous downvoting had to be earned, then the newbie ‘downvoter’ will think longer on the reason for downvoting an answer. The non-anonymous downvoter will be motivated to write a comment in a polite, logical, coherent manner.
If users can't verbalize why they cast a downvote, then perhaps that's a good enough reason for not casting one in the first place.
Another advantage for making anonymous downvoting an earned privilege is that when an answer or question does receive an anonymous downvote, the user knows that the vote was cast by an experienced member. Someone who has had learnt the ropes, and has over time recognized the difference between a weak and a bad/false answer.
Drawback
Revenge downvoting. And AFAICT that is the second proposal's largest drawback. It is pointless flagging downvotes when it is limited to only two or three posts, the mods cannot do anything. The system; however, does "protect" users from serial downvoting, but it is not infallible. The ‘voting fraud detection script ’ is a well-guarded secret, see the links below for further details, so I would not advise circumventing the script to test its limits. Please, don't. ☺
What is serial voting and how does it affect me?
Consistent serial downvoting now avoiding detection
Victim of Serial Downvoting
Protection against revenge downvotes
I've tried coming up with my own solutions, e.g. freezing a downvoted user from voting for a short specific period. But I can imagine that being terribly complicated to put into practice, and in turn, this counter-measure would be abused. Maybe it's not worth it. Maybe we should be adult enough to support the sting of a downvote.