:::As proof that "we don't know what we don't know" (thanks Mr. Rumsfeld), I offer nothing...because as we are saying negatives cannot be proved.  But if we haven't discovered something yet, did it never exist?  This is an equal logical fallacy.  Both sides of these arguments are using false logic i.e. because it hasn't been found and the evidence doesn't exist, it does not exist (your "default" position), this argument doesn't work any more than the pro-Mormon stance trying to prove the evidence hasn't been found yet but "it says so in my book".  Regardless, there are ongoing discoveries all the time in science that were assumed false or nonexistent or impossible in the past yet mystifyingly they are found, or proven, etc. 

 There is much work still to be done in North American archeology.  For example there is study on the very subject you make absolute claims on: the smelting (or just melting) of copper.  Try this one website: http://www.iwaynet.net/~wdc/copper.htm  I make no claims of veracity, but strangely enough there are many questions here...not all copper was hammered...not all was native, some was obtained from ore (which when left in an oxygen starved furnace, (i.e. a kiln for pottery) beads of pure copper sweat out of the matrix).  This discovery of copper smelting was made at differing times in different civilizations including as early as 1000 BC in the Andes mountain regions of North America see http://www.uofaweb.ualberta.ca/newtrail/nav03.cfm?nav03=60986&nav02;=60985&nav01;=60925.  In other words...we don't know what we don't know so therefore the fallacy falls on both sides of this argument, the non-LDS scholars cannot prove the non-existence of something any more than the believers can prove the existence of something not found.  Both arguments fail.