I have had the same experience of a negative review being rejected by RVparkreviews. I told the story that happened to us at a campground involving the staff and management and this review would not be accepted, but I was informed that if I reworded the review as more descriptive of the campground, I could include negatives that we encountered. The re-written review was accepted but it did not have the impact that the original review that I submitted had and lacks the warning that this can happen to you.
So bottom line is negatives are OK but how they are worded can result in a rejected review. I agree that this waters down the value that many feel the site has (or had) in choosing campgrounds.