An uneducated public might be running such proprietary clients for daily transactions as dictated by their governments, but none of them are doing any significant work on the block chain, for that you need big iron.
I think your defence here is based on the assumption that 'the good guys' will have the majority of the usage and/or mining capacity and therefore will be able to take action. For instance you wrote about "culling connections [miners] no longer trust". But this would not be effective because Patriot Edition would already have culled those connections itself. Indeed it was quite happy to do so. It only trusts the Patriot Edition blocks and simply ignores miners which aren't in the Patriot camp. It wants a permanent fork because it has control over a large enough share of the network to 'own' the critical economical mass.
The key here is that exchange and service providers were coerced first and Patriot Edition was playing nice at that time. This helped create a large install base for Patriot Edition without causing the fork just yet. Like you said, if the fork happened too soon, the healthy parts of the network would isolate it and disable it, limiting its damage to just the small install base it had. No, only once sufficient mass was built up the '0 day' switch would be thrown.
By the time the switch has been thrown the majority of the money, and more importantly, the actual usage points for the money, will be in the Patriot camp. 'Big iron' miners will find that the economical incentive to continue mining will be on the Patriot side - that's where the majority of the transaction fees are and more importantly Patriot coins are worth more since the majority of service providers and exchanges switched to the Patriot Edition. The miners will switch, and those who don't will again be in the small side of the fork, a shivering shadow of Bitcoin's former economy.
Certainly I might misunderstand the technical details, but I think on the social side of things the Bitcoin system is based on the idea that most users - miners in particular - will run software which upholds the rules. But if the software could slowly be replaced, like a disease, all those rules could fall over night.