Recently @Catija replied to my answer (https://meta.stackexchange.com/questions/393127/if-more-users-could-vote-would-they-engage-more-testing-1-reputation-voting-on/393275#393275) about mandatory downvote reason (especially for 1+ rep users).

> “I'd be more open to a multi-select for low rep users that allows them
> to pick valid reasons to downvote without giving a free text field.”
– [Catija Staff Mod][1]

The idea is not new:

> consider **adding the quick list of reasons**, so they don't even have to
> type. Possibly **add an "anonymous" checkbox**, defaulting to checked.
>
> [John Saunders Jul 4, 2009 at 12:50][2]

 - The dialog can be shown to any users (not only low rep)
 - For those, who have enough reputation to add comments,  another option with free text  “your own comment” can be shown.
 - If the user already added a comment or upvoted one of existing comments, dialog can be suppressed.


Two points suggested in the comments by Aaron Bertrand, Staff
 - the proposal will be more valuable for answers, rather than for questions.
 
 - the downvoter name if they chose to be anonymous will not be shown on the site, but (in particular for free text comment) should be recorded in the system to be available to moderators if there is an abuse.

I found a couple of suggestions that were deleted just because they were posted as answers instead of as a feature requests:

https://meta.stackoverflow.com/questions/357436/why-isnt-it-required-to-provide-comments-feedback-for-downvotes-and-why-are-pr/362930#362930 (the link may be not visible if you don’t have enough Stack Overflow reputation)

> Please include a reason for the downvote:
>
>  - Too verbose
>  - Argument is unclear
>  - More research required
>  - Issue not addressed
>  - Duplication
>  - Other
>
> Obviously there will be differences in popup layout & content for
> questions versus answers. **Closing the dialog without providing an
> option will be marked as _Other_.**


https://meta.stackoverflow.com/questions/357436/why-isnt-it-required-to-provide-comments-feedback-for-downvotes-and-why-are-pr/401916#401916 (the link may be not visible if you don’t have enough Stack Overflow reputation)

>
> * keep down/up votes anonymous
> * when you vote on a question or comment, a small popup opens, and you get to click on what applies to you (at least one choice). For
> instance for an answer, it
> is:
>
>     * technically wrong
>     * off topic
>     * not justified enough
>     * a repeat
>     * outdated
>     * incomprehensible
>     * ...?

I searched for similar questions and many of them were closed as a duplicate.
My suggestion is not a duplicate of https://meta.stackexchange.com/questions/135/encouraging-people-to-explain-downvotes that was completed in 2009, but a new **feature request** to improve the current implementation.

<hr>

### Some clarifications based on comments and answers feedback

The idea to [Encouraging people to explain downvotes][3] is very popular (1245 votes). This suggestion is how to encourage them more with
 - **less effort** (no need to type),
 - allow to keep **anonymous** and
 - allow even for those, who **don’t have enough rep** to post free text comments.

There are 246 questions linked to/from [Encouraging people to explain downvotes][3]. Many of them are closed as duplicates, but the big number is a clear indicator that the current system behaviour is not good and requires improvement(s).

The FAQ accepted answer https://meta.stackexchange.com/questions/325416/why-isnt-providing-feedback-mandatory-on-downvotes-and-why-are-requests-sugges explains the reasons of the current implementation. However, most of points are not convincing. They may be  redesigned and conclusions may be challenged.

The difference with good  suggestion https://meta.stackexchange.com/questions/353141/explaining-downvotes-a-new-take-on-things is that proposed implementation is different. This request also intends to address the requirement to ask for downvote reasons for people with minimal reputation.

  [1]: https://meta.stackexchange.com/questions/393127/if-more-users-could-vote-would-they-engage-more-testing-1-reputation-voting-on/393275?noredirect=1#comment1315308_393275
  [2]: https://meta.stackexchange.com/questions/135/encouraging-people-to-explain-downvotes?noredirect=1&lq=1#comment4016_2373
  [3]: https://meta.stackexchange.com/questions/135/encouraging-people-to-explain-downvotes