Any concession or collaboration with Berlusconi will only displace the barycentre of the political spectrum to the right, something that Veltroni has already done by excluding the historical Left from a prospective coalition. Veltroni's gamble was to build a conservative center-left party that would erode centrist votes from the right. In that he has failed.
Need we continue to ask? Fai de bèn a Bertrand, te lou rendra en cagant
What the parties need to internalise now is that they have eroded their base of support.