Nothing prevents them from building PayPal, except the regulatory regime they don't want to ascribe to. Also, the currency conversion to their own units and bac

Nothing prevents them from building PayPal, except the regulatory regime they don't want to ascribe to. Also, the currency conversion to their own units and back relates to the taxability of said currency and the inability to use WoW gold to buy Starbucks. It is a matter of degrees - Facebook could seriously destabilize monetary policy for certain countries and subvert currency controls.