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.
Some subgroups -- motivated groups who seem to have endless free time and a lot of passion to click little arrows and leave comments -- brigade and basically remove any functional utility of likes, dislikes and often even ratings. Hateful groups tend to particularly dominate, and weird agendas dominate.
The ultimate solution is, sadly, even more of a filter bubble: If I could click a button and have every like/dislike by pernicious players (in my opinion) completely removed from any measure shown to me, I would respect online ratings better. And maybe, eventually, given that the majority of people are rational and have better things to do, the bores might get bored of trying to manipulate every measure.