I just got into a chat with Amazon's Kindle support and told him I've occasionally lent a Kindle to a friend with a book he wants to read on it, as well as any other books which might already be on that Kindle. I explained that someone said that it was wrong to do that and I wanted to find out if Amazon has any issues with it.
He cautioned me that the person I lent it to had access to my account, gave me a couple of ways to avoid that, and then said Amazon had no issue with me doing that.
So while the lawyers and philosophers and judges among us may see issues with this, Amazon doesn't. By the way I made a similar check when this came up on either this or another forum a couple of years ago and got the same answer.
If this doesn't settle this issue I plan to consult a priest, a rabbi and various others from on high. If even that doesn't settle it I may give up.
Barry