Utility can determine whether it's worth the effort/expense to run a
public archive, but your utility never undermines my rights as an author.
We're very deep into Junior Lawyer territory here.
You might want to review RFC 3978, section 3.3a, in which contributors
make a:
perpetual, irrevocable, non-exclusive, royalty-free, world-wide
right and license to the ISOC and the IETF under all intellectual
property rights in the Contribution:
This is unrelated to how long I-D's stay in the public archive. If
you're not willing to accept those terms including the perpetual and
irrevocable part, you really shouldn't be submitting I-Ds or sending
mail to IETF mailing lists.
R's,
John