"The idea that sovereign bond purchases need to be "sterilised" to prevent inflation illustrates that the ECB has a very peculiar concept of sovereign debt, in contrast to its idea of private debt. Consider the ECB's own covered bond (“Pfandbrief”) programme. In May 2009, the ECB decided to buy up to €60bn of asset-backed bonds issued by Eurozone commercial banks, without much protest. A year later the mere suggestion that the ECB might purchase a comparable amount of sovereign debt was, and continues to be, met with hysteria (...) The constituent rules of the eurozone appear to be based on the bizarre idea that sovereign debt is toxic until such time as it has been sanitized by going through the bid-offer spread of a major investment bank, while privately-issued covered bonds are pristine, even at issue"
Miguel Carrión Álvarez, A Critique of ECB's Liquidity Policies