The Stackitis. A disease. An affliction. 
But what is the root cause of needing a steady inflow of Ag to sustain life? Could greed be the root? Is Stackitis the consequence of an obsessive need to stockpile wealth?
Yes, silver is real money and so it represents one's wealth and the accumulation thereof. But we have seen firsthand how generous the SSG crew - as an example - is with its plata, enthusiastically sharing it far and wide, with friends and strangers alike. So, greed is out, for now.
Silver is shiny and alluring to the Stackitis patient, like a Kastmaster to a spring trout. So is it the aesthetics that reel us in and keep us hooked? Maybe to some extent, but this explanation assumes stackers' brains are functioning at fish-level: see shiny, bite. While this may be true of myself, the beauty of silver doesn't seem like a sufficiently holistic explanation for the root of Stackitis at large.
I recently stumbled upon this excerpt from a book on mineralogy that might shed some light on the topic:
[Source: Love is in the Earth by Melody]
Theory: Stackitis has a spiritual basis. We are attracted to Silver (and gold) because of its energetic properties and the power derived from holding it. Those afflicted by the Stackitis are reincarnated Silver Shamans in disguise:
Metal is the vehicle by which the Silver Keeper understands herself and her place in the Universe, albeit sometimes unconsciously. Coins, bars and pours are the Silver Warrior's axe, that which he uses to chop down the Babylonian money system, bit by bit. With his stack, the Silver Mafioso does good in the world; he invests in the children's future. When the Silver Guardian finally rests and has himself a drink and a smoke as he sits to admire his quiver, he is one with Silver.
Or maybe we just greedy mahfackas...