Yes, you are indeed talking about the opportunity cost. Re-uploading the video as your own (with or without ads) would indeed constitute copyright infringement, but without it, it is not.

I'm not sure this fits the definition of opportunity cost either? I understand why you think it does (because it was money not gained that could have been) but the content producer doesn't have multiple options to choose from here. They expect to have X dollars in their account, instead they have X-Y dollars and there's Y dollars in thief's account, because of the actions of the thief, not because of any decision they made.

The crux is in the expectation: they expect that they will make X in a given day, but an expectation is not a guarantee or a right. They also could have made X in a given day, but sometimes that just doesn't happen due to various factors.

I'm not sure to whom you are referring when you say "thief", but I was under the impression that we were talking about a person watching, but not re-uploading, a Youtube video without viewing ads. This person does not have Y dollars in his account as a result of copyright infringement since they simply watched the video and did not put it up for further distribution.

I really just shouldn't have mentioned ad revenue theft at all in the first place, it wasn't that relevant.

I wasn't saying "people who download are thiefs", I was saying "thiefs start by downloading". Then I had to explain what a thief is, and why they really have Y dollars in their account that should have been in producers account. In my other comment the thief is a separate party from the content consumers (so actually there are 6 parties, content consumers is split into those who watch ads and those who download without re-uploading).