Sorry, you missed the analogy. Let me provide an example.
If I make a video of you (that I consider funny, but you consider offensive) against your wishes, and I post it. Then, the video does two things: (i) makes money for me (I know, its not a lot), and (ii) embarrasses/irks you.
Then, you have to the right to sue (i) me - for making the video, if you can reach me, (ii) Google - for providing the platform for dissemination of the video and not listening to your complaints, if you can show that you made an attempt, or there is reasonable cause they should have acted on their own.
If one misses the analogy, a natural question would be why not sue the camera maker (Sony) as well. But, that misses the point that for Sony, there was no mechanism to stop the usage of the camera once it was SOLD with the limited warranty to the user. The computer maker and the video editing software owner have similar "lack of power" defenses - the active video sharing service does not.
Now, the situation isn't that different from a murder, in which case the gun makers are rarely sued for MAKING the gun, but the stores are sometimes for selling to a person who should not have been able to buy the gun. A simple Google search for "gun seller sued" shows up interesting cases.
In short, (i) a continuing involvement in the process, (ii) a power to have been able to STOP the problem are the most distinguishing characteristics of who can be found culpable. Monetary exchange (however little) further reinforces the accomplice liability.
Cameron - just a quick note on your "counterexample".
There is a world of difference between a scorned boyfriend, and a scorned boyfriend who is committing perjury by forging documents and IDs. Force a person to even check a check box "I agree under the penalty of perjury that I did not lie on this form", and see the form responses drop by 99%, even if you were asking about blue and yellow M&Ms.
Secondly, about your link to instructional videos on YouTube - yes, it is great. And if I make one on Costa Rica rain forests, I won't mind paying 5$ or 10$ entry fee to make it public to the world (which Google could perhaps use to check that it contains no X rated content). It isn't a question of conforming to all laws of all nations - simply a question of conforming to a 17 point inspection that is published, and is the reason for the entry fee.