When someone downvotes a certain question or answer shouldn't they be made to comment on the reasons they downvoted? People aren't helping these SE sites by just downvoting.
It is true that downvoting without comment does little to help the poster understand what they did wrong. For this reason the system has a built-in reminder when you downvote to consider leaving a comment saying what can be improved.
However, the fallacy here is that the primary purpose of voting is not to help/punish the poster. It's to judge the quality of the content being posted. Good questions and answers should be upvoted. Bad questions and answers should be downvoted. That's how we attempt to judge how good a question/answer is. It's not a perfect system, since you only get the number of people who think the post is good, not any estimate of how good (or how difficult). But it's alright for some things. In particular, if you think of votes (or reputation) as an assessment of your worth, value, or knowledge, you're going to be needlessly agitated when people downvote your posts. No one is downvoting you, though we might be downvoting your posts.
The tool for helping the poster understand what they did wrong are comments. On this site, we don't have a ton of activity, typically less than 1 post per hour on average. We're not overwhelmed with new posts, so it should almost always be possible to explain your downvotes, and this is the considerate thing to do. Unless you think the poster is posting in bad faith or beyond help, you should explain why you're downvoting. However, this is not in any way required, and should not be because there are cases where the poster is posting in bad faith or is beyond help.
If a post gets one downvote without comment (especially if it also gets upvotes), I'd recommend just ignoring it. Check your answer to make sure there's nothing obviously incorrect, or that your question is on-topic. If there's no problem there, then ignore it. Perhaps the voter missclicked (I've done this myself at least once here, so it's not impossible), or maybe they're mistaken about something. If you're getting multiple downvotes and no explanations, then consider asking here on meta what the problem is.
It doesn't help to not know why you were downvoted, by commenting you help tell the person what was wrong and how to fix it, therefore helping the site and helping the person improve, by not telling you are being a hater. I'm not saying this because I have been downvoted, because I wasn't downvoted that much. It was the fact that I was downvoted without being told a comment. I think that to help the site people should start telling people what they did wrong, by not that's like sticking someone in prison without a trial by no commenting. I am not saying not to downvote because then why should the person change if they aren't being punished, I am just saying that they should comment as well. Because I have no problem with you telling me..... "You were wrong, because blah blah blah blah", I have a problem with you saying "downvote you, and no comment". I expect downvotes on this answer and question but I want comments to, not to say it will happen, I just want.
Sorry if this confrontational.