Most posters are on GNI for a while and should know the rules to post. Some posters push the envelope by posting articles without sources and post beyond what the rules allow.
So why warn posters : Just delete/close posts and send as email informing posters that they are suspended. This is your authority and you have the right to do so. If posters wants answers to reason for suspension, they should read the rules.
Ignorance of the rules, is no excuse.