There have also been cases where a customer violated Amazon's terms of service and lost access to all of their Kindle e-books. Amazon has all the power in this relationship. They can and do change the rules on us lowly peasants from time to time.
Note, there are indeed ways to download your books and import them into something like Calibre (and remove the DRM from the books). If you do some web searches (and/or search YouTube) you can probably figure it out.
Don't do that. Authors make next to nothing from their books. You don't have to support Amazon, but at least buy a paper copy or audiobook to support the author.
Once you buy this, it is truly yours. Nobody can take it away from you. You don't have to agree to any EULA to read it. No account needed, no activation, no sign-up. You can even resell your copy if you want. There are no technical restrictions on it whatsoever. You can enjoy it any time of day, anywhere in the world, and there's no need for an Internet connection.
I enjoy reading dead tree books as much as anyone, and whilest the publisher/distributor can't take it away, there are plenty of ways you can lose access to them. Fire and flood being the two obvious ones, whereas digital books can be backed up offsite. It's also easier to carry many books when they're digital compared to physical.
For books I care about I try to get both a physical and a (drm free) digital copy for the best of both world.
I buy DRM free books off humble bundle. Even if I already have previously downloaded them. I will not give money to anything with DRM on it if I don't have to. These authors aren't getting money from me because they don't offer a product I want (DRM free books). Other sources do have this product so they can blame themselves or their publisher for losing sales.
It might not be legal, but in my book, it is perfectly ethical to pirate a copy without DRM if you already own a legitimate copy (paper or DRM-inclusive)
I'm not buying a bunch of paper books and creating unnecessary waste just to make sure the author gets paid. I guess I could donate them but then the author loses sales that way. I'm certainly not rewarding the use of DRM by paying for it.
You can donate books to the library, you know. They're always looking for more copies of popular books and what they don't add to their collection, they'll resell them and use the money for more books.
Paper books aren't "waste" by any means as they are easily recycled.
Most authors I've heard from (through their Internet posts) don't mind libraries, but they'd rather you enjoy their books legitimately than pirate.