It's just basic common courtesy to say not just that you dislike something, but why you do so. (It's fine to say something is good without going into details, however.)
I agree with you; in fact I generally do write informative comments to nodes I downvoted. But I doubt that that would be a practice that could be enforced. Just consider nodes of trolling content or otherwise good-willing but definitely annoying users to whom other monks already explained what's wrong with their posts. One may just want to downvote them too - if he feels the content is so bad...

In reply to Re: Why downvote nodes without commenting on them? by blazar
in thread Why downvote nodes without commenting on them? by danmcb

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