Like if I download a textbook to read for a class instead of buying it - I could be proscecuted for stealing
Ehh, no almost certainly not (But it does depend on your local laws). But that honestly just sounds like some corporate boogyman to prevent you from pirating their books. The person hosting the download, if they did not have the rights to publicize it freely, would possibly be prosecuted though.
For physical goods there is ‘theft by proxy’ though (receiving stolen goods that you know are most likely stolen), but that quite certainly doesn’t apply to digital, copyable goods. As to even access any kind of information on the internet, you have to download and thus, copy it.