If the ECB ensures that yield spreads between euro-zone countries are completely rigid, it will de facto create eurobonds - but at the cost of the disappearance of market discipline

The ECB wants to avoid an abnormal rise in yield spreads between the peripheral euro-zone countries and Germany. If the announcement of ECB intervention to prevent these spreads from widening leads to rigid spreads (by eliminating the risk of speculation against peripheral countries), then: Peripheral countries' government bonds also become risk-free; If the yield spreads between the countries are stable, it can be considered that there is a single public debt in the euro zone, i.e. a eurobond; But rigid inter-country spreads in the euro zone will give rise to considerable moral hazard (the disappearance of market discipline): it encourages peripheral countries to conduct overly expansionary fiscal policies.