It was some years ago, I think, that this was discussed at some 
length on the list -- so it may be worth expanding on this:

> How reliable  would a list's archives be if they could easily
> be modified? 

It _can_ be done, but as soon as a listowner's done it she 
becomes, de facto, the custodian of an archive which is 
infinitely malleable, and has to deal with all the folks who now 
regret having said something intemperate or stupid five years 
ago.

In fact, I would prefer it were it actually impossible, rather 
than merely difficult (and, given the ubiquity of archives, 
etc., in practical terms it is actually pretty much impossible 
to delete something totally).

> The time to edit a  message occurs before it is sent. 

Yep.

-- Russ
St. Thomas University
http://www.StThomasU.ca/~hunt/