There's two fundamental behavioral paths you're describing here, when you get into the business of closing. You're anticipating the user thinking one, or both of the following things:
- This bad thing happened, how can I fix it?
- This bad thing is happening, how can I avoid it?
The changes we've put into how questions are closed have addressed both, to a degree - it's much more clear to users why their question was put on-hold, but not always immediately obvious why their question might be placed on-hold. That's something I'd definitely like to explore a bit more, but we do have the custom close reasons and comments, which helps to a large degree.
When it comes to duplicates, I think we could be doing much better than we're doing, and I'm working hard to bring some much needed love to that workflow. Focusing on questions when it comes to more immediate feedback and just-in-time help is definitely something worth additional time, I don't think we've hit the metaphorical 'sweet spot' just yet.
On answers, I don't want to think about requiring a comment, beyond the prompt that tells newer users that just unlocked the ability to down-vote that they can leave a comment if they have thoughts on how the post should be improved. There's reasons why even I don't leave comments when I down-vote:
- I don't have the energy to engage the author of the post, I wanted to down-vote something I know contains bad or even dangerous advice, perhaps returning later to engage in a short discussion if someone else hasn't
- I don't want to deal with the 'return to sender' phenomenon where someone obviously agitated goes through my history and down-votes everything they don't particularly care for
- My disagreement is a philosophical, not technical one, and I don't want to make that argument with a diamond next to my name, because some users do perceive this to mean "I am the site administrator and you should think like I think or else."
However, the times that I abstain from commenting are indeed quite rare and it's generally obvious why I cast my vote to begin with.
There's been talk of having anonymous comments optionally accompany down-votes, however, there's a limited amount of action one can take if they can't actually engage with the person that left the comment. It turns out to be not that much better than no comment at all, which makes it not worth the amount of work it would take to implement.
The better thing to do is establish and maintain an outwardly-friendly policy as an unwavering norm with a mindset that folks should hold themselves self-accountable to this. Not everyone will, not everyone can - the Internet is full of socially awkward people. However, for the most part, folks see their contributions well-received or find clear guidance as to how they could be.
Questions, of course, notwithstanding - I think there's room for more improvement there.