Library books on Kindle - returning them immediately - ethical?

[puzzlegal]

Sorry for the terse note above, I was on my phone.

Excerpted from the rules for this message board, for reference.

@Bone

Copyright – Do not use copyrighted material without permission. Fair use guidelines apply and are interpreted conservatively. If you are quoting material it is good etiquette to provide a link to the source. We construe discussion of P2P and file sharing violative of copyright laws. Do not ask questions of the type “How do I get this peer-to-peer sharing software to work?” or “Can someone help me find a copy of (song or movie clip) using peer-to-peer sharing software?” Debates on the legality of this practice are allowed.

Illegal activity or material – Do not post material that fosters or promotes activity that is illegal in the U.S. For example, discussing the effects of illegal drugs is okay, where to obtain them is not.