I think most of them do it as a knee jerk reaction to getting an answer they didn't want to hear. There are lots of people who ask questions just to have somebody else validate what they are feeling or thinking . One way I have noticed to spot some of these "jewels" is that they post a question under "anonymous" but show their e-mail address. Kinda gives a clue to their mentality.

In some cases it could be because the negative rater has a vendetta against the target of the bad rating and does not want to justify the bad rating. In other cases, it could be that the person thinks that the answer is not useful, but just can't say why this is, at least not within the space allotted for comments. Finally, it could be that the person is just to lazy to leave a comment. In any event, it is nice if someone who gives a negative rating also justifies that rating. Without the comment, the poster does not know why he got rated down and can't either correct the mistake or justify the answer if the comment is incorrect. Failing to justify a rating, especially a bad one, also doesn't tell other readers what is wrong with the answer doing thereby depriving them of the information they need to know whether the the rating is justified.

Sometimes people know that the answer that was given isn't totally correct, but can't explain why it isn't with proof. Sometimes they just are mad about the answer they didn't want to get.

All the other answers are great already. Another thing is that sometimes they are just Trolls who want to make this website less useful, through not only rating down perfectly good answers, but also posting stupid, useless questions and giving useless answers.

Here's a new one for you. I do it all the time. But I look for trends before I do it. I look at profiles to see what sort of answers tend to be given by the user I am rating. If the majority of the answers there are bogus, I return to the original answer and rate it. I no longer leave comments on these because it invites abusive retribution. If the answer merrits a comment. I will rate, then return at a later date to comment. If the negative rating and the comment are put in at the same time on an abusive user's answer, they may visit your profile and downrate as many answers as possible. The other scenario is if the user is reputable. I will then rate and comment at the same time. This can lead either to an edit or an explanation of why I might be incorrect. Then I will rerate. If It's a user that's been around a while, but I'm not familiar with them, I simply leave it alone and wait to get to know them a little better, then choose which rating tactic to use based on reputation. Brand newbies (funny, I guess I am one) who come in like gang-busters slamming stupidity get no mercy at all, cause they and their bogus answers and ratings won't be here long anyway. Newbies that seem to be trying hard get either a good rate and a comment or just a comment on how to improve (no rate). Once I get to knwo them better, I adopt the appropriate tactic.

I will usually only give a bad rating if the answer is just rude (What is wrong with you?) Or useless (A question asking what you would do if you got pregnant and someone saying "I would donate the baby to science because I am a guy") I see no point to leave a comment because anything I would say would not be constructive as there is not really anything to be improved upon.

Fear of retaliation?

Sometimes the question/answer just desereves a negative response, and the reason is obvious.

To hide their identity so they don't get yelled at and trampled by people. That's also why it doesn't say who rated you down.

Because they are trolls. Trolls like to do things undercover because they are cowards.

Not all bad ratings with no comments come from trolls. I agree that a lot do, but there are also people who do not agree with your opinion--a great example is this question: http://www.answerbag.com/q_view/139539/392084 A lot of people are simply afraid that they will offend the other person and don't want to have their answers rated down in retaliation (this did happen and it was ugly). However,the AB guys have put a limit on specific user to user ratings to keep another ratings war from breaking out. There are a lot of reason, but coward DOES sum it up nicely.

well they may be trolls. or you never know... they could just disagree and doesnt want to start a big conflict.

I don't always just agree.

because like Angel's answer about Africans, some answers are so stupid or offensive there is no need to leave a comment

They didn't want to tie ratings to comments PROBABLY because there would be negative rating wars. (Someone gets PO'd about a negative rating, goes to the one who DR'd them, and starts hitting all THEIR questions with DRs. THEY turn around and hit back. Friends get involved... See? So ratings (both positive and negative) are separate from comments.

because they can and will

I think it is because someone, after noticing the negative comment together with a downrate, might try to retaliate against that member.

it makes me sad ='(

Because people do not have the honesty or courage of their convictions. All the time they do not have to leave a comment (even anonymous ones would help) Downrates are totally useless and will continue to cause bad feelings. How are we to know WHY or WHAT has been unhelpful or offensive if people do not leave a comment. We are left to summise that it is a DR just for the sake of it or to manipulate the board or people are Downrating you just because you have a different opinion or take on things.

Chicken

Because they're cowards who lack the courage to stand behind their convictions. It's easier to throw stones from the shadows... "Hatred is the coward's revenge for being intimidated.” - George Bernard Shaw Every DR I have given, and I can count the times on one hand, I have always left a message either via answer or comment. I am done with it bothering me too...their "punishment", if you will, is simply being them. And I wouldn't wish that on anyone.

It is their chicken shit way of trying to make people mad, because they obviously dont have the ability or intelligence to hold a conversation to explain why they disagree with you.

Because they want your answer to get the down rating that it deserves, but they don't want to have to fight with you about it. And yes, you will not just say "Okay, that's cool." No one ever says that.

It's part of AB, and part of the "Troll" culture.

It's easier to act nasty when you're anonymous. It's not really a question of "having balls", but a question of being obnoxious under the cloak of anonymity.

Coz they want to keep their profile flawless!

http://redwing.hutman.net/~mreed/warriorshtm/jerk.htm +5 to you

cowards---I did it by accident and admitted all fault was forgiven too Curse the creep.

The honorable thing to do

They know you are right.!!!!!!!!!!!

When I get downrated I don't expect a written explanation, any more than I would for an uprate.

Because they are cowardly little bullies who like to stir up trouble and run.