Pete, the site administrators can see rejected comments, but for now, users can't. It'd be an interesting idea to have a "click here to see rejected comments" button. But, since the stuff that gets rejected is typically name-calling, threats, and spam, I don't think it'd add much to the page.

It's a common concern that people will vote down dissenting opinions; that's part of why we ask "is this a *good* comment?" first. People can mark a comment as "bad", but still "civil" if they just disagree with an idea. And we have a lot going on in our backend algorithms to keep things fair/prevent bias in what gets published.