Screw immoral. They have been pushing for years now to move from media ownership to it being a license (and a non-transferable one at that). So let's treat it like that. If I own a book in whatever form (physical, digitally, or perhaps stored on an e-reader that is broken and no longer supported), that means I have a license which should morally permit me to format-shift, and own that book in whatever other format exists, read it on any device that is capable, and obtain it by any means that does not amount to actual theft, or constitute distribution (like Torrent).
Personally I buy a great many books on my Kobo reader, knowing that most of them will be gone if the service ever ends. Not a big deal. But books I need to reference, lend out, or plan on re-reading at some point, I will either buy them DRM-free, or get a physical copy. I do wish I could get an actual license for them, one that ensures that I can continue reading that book regardless of what happens to the publisher. Right now, that only applies to physical or DRM-free books.