Listen to this post. Users can't just vote to close or whatever and expect everyone to understand. Some of the flagging reasons are hard to understand and if you don't add a specific reason, how are we suppose to know why you voted to close. None of us are mind-readers :)
A good thing to think about is to:
Coach new users that have written a not acceptable post. If it is inappropriate completely(spam, etc) then flag, but just downvoting for a post that is not in scope or some other reason without a explanation is not right. It discourages people and doesn't promote team efforts. I make a point to add encouraging statements and thank them for joining the community, because without New Users or any user we have no community.
Think "Can this post be bettered?" before downvoting or flagging for closing. If the post can be bettered think about ways you can do it and comment nicely on how to fix it. Downvoting and flagging should be left for posts that do not promote changes to problems and other reasons.
I think that not telling why people are closing can destroy a site, as people get discouraged and then just leave. Also, not commenting on ways to fix a problem makes the problem more likely to get repeated again and promoted not quality post in the future. We need to treat every post like its the last one and every user needs to be treated the way we want to be treated.
We make the site we want. That means that if we keep closing, not promoting communication and excellence through communication, then we will soon have no site.