Morally OK: 100% of the time, as long as the ebook is identical to the physical one other than its format. That is, if you could scan and OCR the physical book and end up with the same result as the ebook, yes. If the ebook comes with extra content that you would not have access to without buying it in that format, I would say that's not OK. (Table of contents and indexes that link directly to a page rather than just listing its page number don't count in my opinion. Those are just the electronic equivalents of the paper indexing system.)
Is downloading ever copyright infringement? I was under the impression that it is the uploading, i.e. distributing that is illegal, not receiving the copy.
I feel like some copyright holders would have you believe that both uploading and downloading copyrighted material is breaking the law. However, in practice, it's far more expensive to chase the downloading party as well as far less effective. Stopping the act of uploading stops the act of downloading in many cases.
> For example, you can use copyrighted work for the purpose of research, private study, education, parody or satire. You can also reproduce copyrighted work to ensure interoperability of computer programs or for backup copies.
I do the same with all media I access legally, some of which I definitely do not have a license for. At least I've never seen anyone provide me with a license for anything I am reading on this webpage.
It never really made sense to me to view copyright as dictating what you are allowed to do with something. People do try to turn it into that, but it makes far more sense if you view the act of publishing as the step that is protected by copyright.
Laws do differ on this point but if we want to have any hope of owning anything in a digital world we need to push back against the idea that copyright allows someone to dictate the lives of anyone using their intellectual property.
Pirating ebooks would be a way bigger crime than just stealing, but fortunately they are almost never shipped by boat, so people who want an illegitimate copy of an ebook don’t have to jump on board, kill a bunch of people, and steal that booty.