The dislike button on YouTube videos is one of the few remaining signals that what you are seeing is propaganda. It hadn't occurred to me that this would happen (although it seems obvious) and it is unexpectedly frightening to me. I suppose the fallback will be videos with comments enabled, where people can 'like' a comment who is saying something common sense and reasonable in response to the content.
This was one of the major inflection points for worsening quality of content on reddit, and it will be for Youtube too. For exactly the reason you've described.