We illustrate by analogy to Shimon Peres, Israeli President, who  articulated it well when he said calling off negotiations everything  there is violence essentially gives a veto to the terrorists.
Stephen Walt has an interesting list, that will help to cut through some of the bellicose logic.I disagree the "grand bargain".
There is an IAEA and protocols and treaties. If these do not cover new circumstances, then they are adaptable, through process (they are actually very competent). To admit a need for a grand bargain is to go off the map, IMHO.
Here's one thing to worry the most, right now, about Iran. It's witless enabling of the "hardline track":
There is a hardline in Iran that sees the West's use of dialog as just a means to delay their developing what they see as nuclear "self assurances", i.e. the sovereignty guarantee. Putting aside that that is a false assurance, there are some hardliners in the U.S. and Israel who believe, as always, that only "absolute strategies" or "absolute dominance" can bring security, so they "cannot allow" this or that.
The louder these two factions are, the less chance for finally reaching agreements, important agreements, for Iran to have nuclear materials enriched in a way that minimizes the chances for proliferation and danger.
As far as bright lines, the Israeli hard right and so forth, here's something that Walt himself pointed out recently:
Thomas Schelling's book The Strategy of Conflict set forth his  vision of game theory as a unifying framework for the social sciences.  Schelling showed that a party can strengthen its position by overtly  worsening its own options, that the capability to retaliate can be more  useful than the ability to resist an attack, and that uncertain  retaliation is more credible and more efficient than certain  retaliation. These insights have proven to be of great relevance for  conflict resolution and efforts to avoid war. 
It's sad, therefore, to see Joe Biden proclaiming on what "we cannot allow", from so many perspectives. Why? It makes you easy to manipulate. We illustrate by analogy to Shimon Peres, Israeli President, who articulated it well when he said calling off negotiations everything there is violence essentially gives a veto to the terrorists.



 
