> You could argue that, YouTube has maintained their safe harbour, and hence they're a reasonable entity.
That's not how the reasonable person standard works. "Reasonable person" is a term of art. A reasonable person is a sort of thought experiment that's used often in law. We imagine a hypothetical person who is in most respects like the average person, and who makes sound judgments based on the information available to him or her. We then hold real legal entities, such as website proprietors in DMCA cases, to the standard of this hypothetical reasonable person. For example, we say that a reasonable person running such and such website would have noticed copyright infringement, and thus the website's proprietor was obligated to remediate the infringement.
The fact that YouTube has maintained its safe harbor means YouTube is successful in that regard. It doesn't tell us anything about the legal definition of a "reasonable person."
That's not how the reasonable person standard works. "Reasonable person" is a term of art. A reasonable person is a sort of thought experiment that's used often in law. We imagine a hypothetical person who is in most respects like the average person, and who makes sound judgments based on the information available to him or her. We then hold real legal entities, such as website proprietors in DMCA cases, to the standard of this hypothetical reasonable person. For example, we say that a reasonable person running such and such website would have noticed copyright infringement, and thus the website's proprietor was obligated to remediate the infringement.
The fact that YouTube has maintained its safe harbor means YouTube is successful in that regard. It doesn't tell us anything about the legal definition of a "reasonable person."