From the link Dave just posted to you, this part is very important:
It is also not the Moderators’ role to remove posts on the basis of "truth" or "accuracy". Readers determine the veracity of the posts they read and the credibility of other Posters. If a Moderator disagrees with another Member’s post they have the same recourse as any other User; to ignore the post, or to challenge it with a post of their own focusing on the information, not the other Poster.
In short, the role of the Moderator is to help foster an environment that promotes and encourages posting of ALL opinions and information about companies, regardless of the bullish or bearish sentiment of the posts, and to be the site’s first line of defense in ensuring we remain free of spam, vulgarity, and personal attacks.
I'm sure your next question will be:
"But why do the bashers do it?"
The answer is that unless they violate the TOU, they can.
Have fun,
Phil