High quality answers are the life and blood of our site. If we continually produce high quality content, we'll attract more experts who will want to help fellow skeptics. On the other hand, if low quality dominates the site, an expert who visits the site will conclude this site is a waste of time and never come back.
How can I help?
There are many ways in which you can help. Flagging low quality, offensive, abusive, or hate-filled answers is one way - oh, and spam too. We don't like spam. Please flag it. Leaving comments to other users on how they can improve their posts is another way. Editing works well too.
However, the prime way by which you, the community, affect the quality of the content on the site is voting*. Voting drives the economy on the site. If you see a great post, upvote it right away. By upvoting a great answer, you send the signal that you want more of these and get the user closer to new privileges. Meanwhile, if you see an answer you think is low quality, downvote it immediately.
In other words,
- Upvote great content.
- Downvote answers that obviously wrong.
- Downvote answers without references.
- Downvote upvoted partial answers down to zero.
- Don't upvote partial answers.
Authors of good content should never go unrewarded. Conversely, it should be made clear to everyone that poor content is not tolerated here, that poor answers will be met by a downpour of downvotes.
Upvoting great content is easy. Downvoting is harder - it costs reputation, after all - but it's just as important. The presence of an highly upvoted question tend to deter other users from writing a new answer. If that highly answer is of low quality, that's a huge loss for the site, because we might never get an actual great answer. Downvoting bad answers is paving the way for better, more informative answers, and that makes the site better.
Oh, and leave a comment explaining why you downvoted. With luck, the author will learn from this mistake and correct his post or write better answers in the future.
But what about the rep loss?
While downvoting costs you a tiny bit of reputation, it is still, by a very large margin, a net gain. Think of how much time you've spent on this website already. Think of how much you've learned since you're on this site. Think of how we're making the Internet a better place. As Phil Plait said, we're making the world more reality-based, post by post.
In other words, downvoting is good for you (and for the site)! You trade a bit of reputation on this site for heaps of knowledge and hours of entertainment.
So I say: go forth and downvote!
*Actually, that's a lie. Writing good answers is, but that sentence sounds so much better if I pretend voting is.