Huh? Everyone is liable, to some degree, legally and morally for what they post. It's just that in practice it's hard to enforce.
Whether that falls under US jurisdiction, another country if they're outside, both, etc... for the case of youtube hasn't been settled yet. Though it seems very likely to be trending towards that direction.
I don't understand the relevance of your comment. You've seemingly mixed in a few things related to my point, while ignoring the point itself.
We're specifically talking about legal jurisdiction. An instance of copyright infringement depends entirely on jurisdiction, because copyright is nowhere near any sort of natural law.
I agree that practically the US government will attempt to invent some rationale to bring every action in the world under US jurisdiction (having looked at a Federal Reserve Note once in your life, wearing a shirt that is colored red, white, or blue, etc). But assuming other countries might actually stop acquiescing to this type of nonsense some day, then an individual having explicitly assented to it is likely to be a strong point in favor of continuing to asserting worldwide US jurisdiction.
> An instance of copyright infringement depends entirely on jurisdiction, because copyright is nowhere near any sort of natural law.
This is false for the many countries that have signed on to various binding international IP treaties, such as the various WIPO treaties which the US has also ratified. You should read up on it.
A copyright issue involving an online service such as Youtube in one WIPO ratifying country would near-automatically translate into an issue across many jurisdictions.
China also has ratified the 1999 convention as of last summer, so the area of the Earth where someone can ignore these treaties is shrinking rapidly.
Whether that falls under US jurisdiction, another country if they're outside, both, etc... for the case of youtube hasn't been settled yet. Though it seems very likely to be trending towards that direction.