Judy - I've dealt with looters, pot hunters, privy diggers, etc. on a wide
range of fronts, and I have a hard time defining common ground.  I've had
metal detectors asking where the soil removed during the excavation of a site
will be sent so they can search it, as well as urban sites looted during
excavation by bottle hunters too anxious to wait.  And I've heard from
collectors who have hit sites after the archaeology has been done and
commented on the things the archaeologists left behind.  At an extreme, I'm
aware of an urban site where the "archaeologist" hired for the project
allowed bottle hunters to dig the privies, kept all the non-bottle artifacts,
and took notes on the whole bottles the hunters found and were allowed to
keep.  That obviously is not archaeology.  I agree that once a site has been
data recovered, its significance is gone, but like you am worried that
permitting bottle hunting in anyway sends out the wrong message.  The common
ground, if any, is obviously through discussion and out interest in the
material past.  We are all interested, archaeologists and relic hunters, in
material remains, so discussing material culture, maybe even making urban
labs open for some sort of assistance in artifact identification, might
provide some opportunity to inform one another, and particularly for us to
communicate with the relicers.  One of my best experiences with a relic
collector was in Augusta, where I got together for several visits with a long
time bottle collector and privy digger, and made extensive use of his
collection and library to document the bottles we were finding, all of which
went into our report with acknowledgements.  He was very appreciative of
seeing his vast, but probably never to be documented, knowledge and various
documentary sources published and made of use, and I hope that through my
conversations of the meaning of archaeology he gained at least some
appreciation for archaeology (he was getting on his years and had already
given up privy digging, so I don't know what effects our meetings may have
had on his approach to his collection).
 
I don't have any severe problem with metal detectors collecting backdirt,
since that is unprovenienced material.  But I can't see allowing privies and
other closed context features to be looted after an excavation is complete,
because that sends out the wrong message, even if our funds are spent and we
haven't collected every artifact and feature from the site.  I think the
common ground has to be our interest in material culture, but we still have
to push for the importance of archaeological context and documentation and
cannot endorse or accept the undocumented looting of features at any time.