When norms like guest right or the sanctity of envoys are put in jeopardy, as the Lannisters have done, what does it take for those things to be respected again? And as an aside, where do you fall on the Blackfish’s conduct at the Second Siege of Riverrun, in choosing to fight to the last man?

To me, it would take the violation of those customs having consequences. If I’m right about Red Wedding 2.0, I think the destruction of Houses Lannister and Frey will be seen by the masses as the wroth of the gods visited upon the impious. 

In terms of the morality of fighting to the last man, it’s hard to say. Ultimately, I think it comes down to the cause you’re fighting for and what your alternatives are.