Then demonstrate its orthodoxy rather than asserting it. 

It scandalous to suggest that the previous Popes, Saints, and Fathers and Doctors of the Church who supported capital punishment were motivated by “legalism” and a “concern for preserving power and material wealth,” and that they lacked a "deep understanding" of the Gospel. 

The ambiguity?

In his statement, Pope Francis cites Pope St John XXIII’s statement that “the Church should never depart from the sacred patrimony of truth received from the Fathers.” He also agrees Pope St John Paul II’s remark that the Catechism “take[s] into account the doctrinal statements which down the centuries the Holy Spirit has made known to his Church.” He goes so far as to assert that in saying what he does about capital punishment, he is “not in any way contradicting past teaching” and that the view he is advocating “in no way represents a change in doctrine. ”

Go figure! Let's see him declare his personal opinion  ex-cathedra,