If he's right that there's something close to a consensus on this, it would be good to have it summed up in a handy way. May I suggest the following: when genocides are in progress, the killers should just be allowed to get on with it. This humane conclusion will surely hold its own against the generations of writers on international law who have held that in certain extreme circumstances intervention on humanitarian grounds is justified. But I guess that's just the idea 'in theory' that the consensus folk profess to like. In practice, better to dump it.
Geras' suggested maxim has the benefit of pithiness. It would also save me the trouble of finishing my dissertation. Unfortunately, the moral truth may be more complicated.