The original note, as written at the time
Have you ever noticed it is not possible for you to mass unlike all the videos that you’ve ever liked on YouTube, or all the content and comments that you’ve ever liked? Unfortunately what this means is that you would have to go item by item. And yet this content is what the algorithm uses to feed you new information.
Ongoing development
Have you ever noticed that you cannot mass-unlike everything you have ever liked? On YouTube, on any platform — the only way is item by item. And that history is exactly what the algorithm uses to decide what you see next.
This is not an oversight. It is the most quietly profitable absence in consumer software.
A like is presented as a small gesture of appreciation. It is actually training data, given freely, by a person who believes they are expressing a preference rather than shaping a feed. And the reason there is no undo is that undo would cost the platform the thing it most needs: a record of who you were before you decided to change.
The asymmetry is worth stating precisely. The platform can change what it shows you, retrospectively, without telling you. It can change the meaning of a like, reinterpret it, resurface it to you. You cannot change what you gave it. One direction of memory is a service; the other is a mechanism of control.
A mass-unlike is not really a feature request. It is a demand for the right to revise your own record.
What would be honest is not a button. It is a visible history: here is everything you have liked, here is what the system inferred from it, here is what to delete. That would be expensive to build and terrifying to ship, because most users would look at it once and be uncomfortable.
The measure of a platform’s respect is not what it lets you post. It is what it lets you withdraw.