But the thing is that we have come to a point where I don't think any of these likes/dislikes is about expression of any opinion at all. To me, it's often a pure reaction, with barely an analysis of what's being said, but rather about what others may think of it (and we have a tendency to follow them, not to appear as a black sheep : "Everyone dislikes it, so I should dislike it too", or the contrary..).
Not very interesting...
Disliking a video on YT was anonymous I think, so I can't see how social pressure came into it. I liked a video if it was good, I disliked a video if it was bad, or I did neither if I was indifferent.