In a 1999 presentation for the Montreal Institute for Genocide and Human Rights Studies, Professor Frank Chalk noted five circumstances that would allow the maximum intensity of a media-driven response to a crisis:
the introduction of a new medium of communication, such as radio [or Twitter];
the use of a completely new style of communication;
the wide-spread perception that a crisis exists;
a public with little knowledge of the situation from other sources of information, and
a deep-seated habit of obeying authority among the target audience.
All of these circumstances pertain to the promulgation of the genocide in Rwanda in 1994 and many of them are found in other cases of genocide and genocidal killings, as well.
It's easy to see how well this model applies to the Iranian situation, too.
This shouldn't be read as an indictment of social networking technologies in general, or of Twitter in particular. As I said at the outset, I'm thrilled at how critical this technology has been to the viability and potential success of the pro-democracy demonstrations. As the cat-and-mouse game around proxy servers further suggests, the only way for a state to entirely cut off the use of these kinds of tools is to kill its own information networks, blinding itself and effectively removing itself from the global economy.
What I'm arguing, however, is that we shouldn't see the positive political successes of emerging social tools as being the sole model. We should be aware that, as these tools proliferate, they will inevitably be used for far more deadly goals.