Why taking so much time to nationalize the banks?

According to Nouriel Roubini, the only solution to clean the toxic assets from the global banking system is to nationalize banks. See his comments on: http://www.rgemonitor.com/roubini-monitor/255546/nationalize_the_banks_were_all_swedes_now
I think he is right. To what extend the Obama's administration will have the courage to move forward to that solution? If the toxic assets are not cleaned within the next 3 months we will run into a stag-deflation economy (near depression) and we might be stuck for 10 years in an economic crisis.