For me, this excerpt from the protest of the seven French SSPX deans (one of which -Fr. Gaudray- was a professor of mine in Winona) says all I need:
"...we reply that the state of necessity which legitimates our way of doing things is not canonical, but dogmatic, and that the impossibility of having recourse to the current authorities is not a physical, but a moral one."
In other words, I'm fine with canonical arguments, insofar as they are applicable (e.g., the moral imposibility of obtaining a conciliar delegation satisfying the "grave inconvenience" clause of 1098), but they often will close off avenues of survival -contrary to their purpose- precisely because as St. Thomas says, laws are written for ordinary times, and necessarily leave out of consideration circuмstances which happen only rarely.
For me, the stronger argument is always dogmatic and doctrinal (e.g., necessity, epikeia).
I realize nobody is denying this, but just wanted to bring it into the conversation, unless people paint themselves into a corner by only entertaining canonical considerations.
PS to Mith: Looks like we were typing at the same time.