This is actually why disinformation works so well. Many people are consumers. A handful of people create content. Everyone has an expected behavior in a rather fragile system. If an organized group comes in and acts in a way that is outside of the system norms, they can very much control the dialog.
I did a project on this during my Masters.  Reddit has an option to display your upvotes and downvotes publicly. About 2% of users have this option enabled. I scraped a random sample that I found from the torrent of all Reddit posts and comments. I looked at pairs from that set that shared common votes and the highest pair was from /r/the_donald. This behavior is what allowed it dominate the front page for so long. When most users are just voting on 1 or 2 things per page, and someone else comes along and votes for every post they see, it can greatly affect what is displayed.
When you have a small set of people controlling a conversation, they can manipulate what a huge number of people consume. Social media is an incredibly effective propaganda machine!