As I wrote the other day for the Christian Science Monitor, the decision to exclude Iran from the Montreux talks is a huge diplomatic mistake.
Tehran’s help could be crucial in forging a coordinated diplomatic strategy for resolving the crisis in Syria and enhancing regional security. As a major backer of the current regime, Iran has enormous potential leverage in Damascus.
Iran’s goal in neighboring Syria is to have a regime that is friendly to its interests and that protects the Alewite community. But this does not mean Iranian officials are wedded to the discredited Assad regime. They might be willing to consider an alternative arrangement if it addresses their needs.
It was unwise for the U.S. to insist that Iran publicly commit to replacing Assad before the talks begin. Insisting on preconditions for negotiations is not the way to successful diplomacy.
Tehran shares Washington’s goal of ending a war that is causing widespread instability and violence in the region. Iran also shares the goal of ending the growing threat of Al Qaida-based militancy in Syria.
By inviting Sunni-dominated Saudi Arabia to the negotiations but excluding Shia-majority Iran the United States is taking sides in a regional ethnic power struggle. This could exacerbate the deepening Sunni-Shia divide and further undermine security in the region.
Washington would do better to adopt a more even-handed strategy that seeks to balance differing interests and works toward more inclusive power sharing in Syria and across the region.
David Cortright 
Yes, they should!
I am of the same opinion; the U.S. made such a decision because its clinging to the notion that the war in Syria is still about democracy… Whatever solution they come up with through such means will only be temporary just like Egypt’s was. The all-inclusive way always wins but is recognized when the seams of a solution start ripping…
The US and her allies made a terrible blunder by excluding Iran in the summit. Iran can convince the Assad’s regime if her interests are guaranteed in any future resolution of the conflict. In other words, Iran has more leverage on Syria then the US.