There is a big difference between deleting negative posts and deleting posts that are just rehashed versions of previous posts, I don't believe that posts are deleted just because they are negative. It would be nice if we could have some originality in the original posts not more of "bitcoins dying, bitcoins a scam etc etc"
When you consider the number of posts and replies to them, the moderators do a pretty good job but naturally they may miss some that need deleting and delete some that don't.
I would like to see more discussion on how we as a community can promote Bitcoin and explain to the uninitiated that Bitcoin is here to stay and is the future.