"Spedaro relates how the pope wishes to distance Catholicism from any suggestion that it is a guarantee of power, any lingering vestige of Constantinianism". 

This seems to be key, sadly but realistically, more threatening to the authoritarian, rotist and ideologues of religion and political right than the more easily debatable "mercy".  Detractors can argue forever about mercy without justice, i.e., vindictiveness, and thus obscure the reality that it is about alliances of mutual advantage in regaining, maintaining and enhancing power,  control and the benefits thereof.  Constantinianism, joint control over the body and soul of community to the advantage of elitists is, it seems, the essence of the strange "ecumenism" of hierarchy, evangelical christians and right wing politics. 
Mercy as the discerning, unwavering, loving benevolence of Jesus is meant to be the thorny conscience in the side of state, not willing conspirators in domination, an unholy alliance. "Render unto Caeser..."