Banks know as well as anyone - well, probably better than the average person - that the Fed's dollar debasement policy will eventually push serious inflation into the economy. Inflation destroys the value of fixed income instruments. Banks have every reason to be concerned about how badly inflation will hurt the book value of loans they've issued. Holding hard assets on their balance sheets can ameliorate the effect of inflation on their loan portfolios. How much it will help will of course vary by institution, but those TBTFs that went hog-wild with home mortgages have the most to lose from inflation. They know who they are. BofA's rush to buy Merrill Lynch may be a saving grace if the bank can hold onto whatever hard asset store Mother Merrill is allowed to retain..
The Fed may not have much choice but to accommodate banks' desires to continue holding commodities, even if they are restricted in trading them. Think of a hard asset hoard as a balance sheet backstop that gives the Fed time to delay further QE. Keeping this grandfather exemption for bank holding companies will give the Fed room to focus liquidity backstops on banks that didn't do much trading with commodities. Helicopter Ben needs to think about how he can make the Fed's job less difficult as we approach the next round of the financial crisis. Think hard, Ben. Think hard assets.
Full disclosure: No positions in any company mentioned.