Well my suggestion would be to be confident and positive. Confident that your issue/ cause/subject is important and that there are enough other people sharing that believe in the forum, regardless of the nay-sayers. With positive I mean post things that are on topic for you, comment on things you find contributing to the issue/cause/subject and refrain from the rest. You really don't have to tell people that something is inappropriate, that they are wrong, dangerous. They will learn by not getting a response. Don't try to control a narrative, try to share a narrative with as much people who are willing to join the forum.