First of all, I think we need to establish and agree on the assumption that the Uchihas were staging a coup. At least then we're all talking about whether or not Itachi picked the right side to protect.

And honestly, if a guy agreed to wipe out his entire clan on the premise that it's saving the rest of the village.. I'm pretty sure a guy as intelligent as Itachi would have made sure he wasn't acting on someone's guess.

I had totally forgotten about the whole Uchiha-being-isolated thing.. but it still doesn't make Itachi's decision any different. To him, both sides are villagers from Konoha. It's just a matter of picking the action that causes the least casualty (given that the killing of one side is unavoidable), then following that path.