I happen to agree with your evaluation. However, if I try to evaluate things from a neutral ethical standpoint, I can see a potential dilemma in caching when material has been retracted from publication.

However, I feel that the value of memory-augmentation, combined with the value of preserving information in case an author is pressured (legally or otherwise) into removing it from publication far outweighs any potential harm that might be percieved by copyright-holders.

I also see it like ripping CDs I own to my harddisk - I am making an accessible copy of something I have a right to access. If my CD is destroyed, it is still ethically correct to keep my Vorbis files. Likewise, if content is destroyed from the 'net, I see no issue with maintaining the cache of it.