Typically, I prefer using comments as well. Voting up/down sort of sends the wrong message to new users, even though as Zanna explained it is not intended to be a form of punishment/reward, but people see it that way. Well, OK, maybe it actually is intended. StackExchangeStack Exchange is sort of built on the game principle to retain users; to quote Jeff Atwood - one of the creators of Stack Exchange - from his blog post Gamification:
It is true that all our stolen ideas about reputation systems, achievements, identity, and vote scoring are in place specifically to encourage the adoption of the brave new no-nonsense, all-signal Stack Exchange Q&A model. Without those incentive systems, when left to their own devices, what you get is … well, every forum ever created. Broken by design.
So now - questions. "Is it generally a good idea to down-vote new user answers?" Voting on answers is always a good idea, but new users may not be familiar with the whole system of Stack Exchange. Good idea and intention, but if the user doesn't understand its purpose, it leads to bad results. Sorry, but as much as I like Stack Exchange and Ask Ubuntu, this is not the most intuitive site to use for the beginner. So as far as new users go, it is better to do the following:
Comment to say what the user did wrong and how they can improve. This will do much more good than just downvoting with no explanation. Make it a learning case for the new user.
Use the gamification idea and positive language in comments. They'll listen to you if you talk to them in encouraging way, rather than offensive "You're wrong, n00b!!!". For example, something along the lines of
Welcome to Ask Ubuntu! Please edit your answer to clarify which exact module the user should remove. It is best to provide exact steps which the question author could follow.
Once the user gets past a certain reputation barrier - maybe 50-100 points - they should be familiar with how the site works and the purpose of downvotes. So it is OK to downvote the answer if it is incorrect, wrong, low quality, or off-topic. For new users, a downvote (and probably deletion) is warranted without a comment only if it is spam, a security risk, off-topic, offensive, or a question - not an answer.
how do we convince more low rep-moderators to leave a comment rather than simply downvoting?
FYI, there's no "low-rep moderators". The site is designed to be self-moderating by the community. Actual moderators step in in cases where the post is offensive, the user has crossed behavioral boundaries (and it is ban-hammer time), etc. The way to convince people is pretty much the same as in any other place:
Give them an example to follow; do leave comments yourself, let others absorb your behavior
Give them incentive; add +1 to the comment if it mentions good reasoning for why the answer is downvoted
IMHO there seems to be some irrational fear of new users and their so called "clutter" and "poor answers". New users on the other hand get frustrated because of downvotes and take it overly personally. Neither is a serious issue. Just focus on "playing the game without playing it", if you get what I mean.