Earlier I asked What's the point of voting on questions (especially downvoting)?. From this question, I understand that down-voting (questions at least) seems to be for general house keeping among other things.
This question is more about down-voting answers especially those of new users. I see a lot of new users who try to answer questions who maybe don't have all the information necessary (as they can't comment to find more information) or they don't really know what a good answer looks like.
These answers (based on my personal experience) inevitably get down-voted to the depths, often with no comments. I don't always agree with this as I think it is great that new users want to get involved in contributing and it's unfortunate that they are ultimately met with some form of disdain. And they don't know what they did wrong.
Rather than down-voting the answer, I personally prefer to leave a comment detailing what they did wrong, and if it is really bad, generally flag it as well .
So my question is, is it generally a good idea to down-vote new user answers? And how do we convince more low rep-moderators  to leave a comment rather than simply downvoting?
 I will say that I consistently see a few users who do in fact do exactly this as well but they all seem to be quite high-rep users and I can't say whether or not they personally down-vote as I don't know who up/down votes
 I say new user as I think veteran users should know better about how to post, and these generally get down-voted for misinformation or god-awful formatting (again based purely on anecdotal evidence)
Edit 1: I would like to add that I see a lot of this behaviour in the First Posts review queue
Edit 1.5: I'd also like to add that I don't have a problem with downvoting answers of any user if it is a bad answer. My problem is downvoting and not leaving a comment (when no one else has commented) detailing why it was deserving of a downvote and how to improve it. Or better yet, as mentioned in one of the answers, edit it yourself to improve the answer.
 Edit 2: By "low rep moderator" I was more meaning those with access to the review queue. Often when going through it in the morning it is quite empty, and I often run into answers in the wild from new users that have been down voted to the depths which are often easily fixed ie they merely posted a link to a solution rather than taking the time to type out the solution themselves, or some misinformation.
I think a good example would be my most recent answer to a question, Measuring performance with shell I made a couple of blunders (forgetting which shell I was in and referencing the wrong help/man page). Rather than downvoting I was left a few comments detailing what I had done wrong, and it seems new users aren't granted the same liberty. (Granted the comments were from those I referenced earlier who tend to do the same as me)