I call downvoting without leaving a comment cowardly downvoting, since the downvoter didn't have courage to express/formulate their critique of the answer in the comments. It might be that they even do not understand the answer.
Some reasons for cowardly downvoting
There may be multiple reasons for such downvoting:
- Some users treat upvote/downvote as like/dislike buttons on social networks, i.e., they do not realize that votes on SE are an equivalent of peer review in scientific community - they are not to express whether the answer pleases us, but to signal to other users whether it is correct or not. (Note also that many social networks nowadays do not offer a dislike button, to avoid bullying.)
- Sometimes downvotes come due to competing interests - the user may have also published an answer, and wants their answer to appear above yours, which may potentially bring more upvotes. Such competition may become especially sharp when dealing with bounty questions.
- It may be a user that you have recently argued with about something else, and who is now taking their revenge, without any relevance to the content of your question.
- Finally, in some cases downvoting is a form of a collective punishlment - the user may not like the question or the topic in general, and they downvote everyone's answer to discourage the discussion.
Remark: I do expect a few random downvotes by people who are offended by what I have written above - which would only confirm the points made.
Suggestions for principled downvoting
Here is the practice that I suggest for dealing with an answer that you do not like (which pretty much follows the tradition in scientific publications):
- Write a comment on the answer, explaining what you think is not correct. This way you a) give opportunity to other users to understand the issues and participate in the discussion, and b) give opportunity to the author to correct themselves or argue for their viewpoint.
- If you have discussed the issue with the author, and you still believe that the answer is incorrect/misleading, then downvote. Note however, that you will negate everything that is contained in the answer - so downvoting because of a minor issue, while the bulk of the answer is correct, is not necessarily a good idea.
a few clarifications in view of the discussion in the comments:
- The main point of this answer was to stress the importance of leaving a comment when downvoting, not to discuss particular motivations.
- My least of reasons for downvoting that I consider illegitimate was not intended as comprehensive. I added qualifier "some" in the preceding sentence.
- There is disagreement about some of the reasons cited, at least to rhe extent that they are not excluded by SE policy. Still, others are clearly beyond the pale. Sadly, no one seems to have a problem with those (judging by the downvotes.)
- In any case, it is important to remember that everyone carries a moral responsibility for their own actions. When you downvote, it is your downvote. You own it, even if no one know.
The reactions to this post seem to focus on only one type of situation - where obviously low quality content is downvoted by a high-reputation user. This was not however the situation that I had in mind when writing this post, as I hope should be clear from (re-)reading it. Given that most of the members in this community are either students or non-physicists, it could be very well that high-quality content is downvoted by the users who do not even understand it - due to the lack of background (general or specific to the question discussed) or due to not bothering to read the context freely. I wonder, if statistics is available on the number of downvotes by the reputation of the downvoters and the downvoted.