My exact point was that this was closer to diffusing a bomb you happen across than a good Samaritan law because of the collateral damage potential, which we normally assess the tradeoffs of through collective means such as government, and because it's a non-emergency situation.
Good Samaritan laws only apply to emergency care rendered to people in need of it (and only if they don't refuse). You wouldn't even be covered if you grabbed someone's broken arm and tried to set it without permission. (That would actually be assault, for which you'd be liable.) You definitely wouldn't be covered if you unilaterally released a protein in to the atmosphere because you suspected it would stop the flu. You'd probably get charged with using a WMD if it backfired and people got sick.
I think people who are arguing that it's a good Samaritan situation are simply being selfish, because they don't want to have to consider how their actions might impact others or act with restraint and professionalism.
There are plenty of ways to proceed with getting help from security consultants even if there is liability -- eg, confining their actions to a single network and being indemnified by the owner.
Globally poking a widespread infection without a care in what the infected prefer is emphatically not what Good Samaritan laws are meant to protect and should carry global liability.
Ed: To address the question under me, since I'm "posting too fast" --
My problem is that many of these FBI programs exist in a legal limbo -- the researchers are working with the government, but I'm not sure they have the kinds of immunization agreements that government contractors usually get (eg, that you have to sue the government not the contractor since the actions are taken under government authority because you're working for the government) nor that they have to observe the restrictions placed on government actions. Too much of cyber security exists in these (intentionally) gray areas.
I dislike this Wild West state of affairs and want the matter of liability and restrictions/accountability to be directly addressed, even if it's just making de jure the de facto situation. I think cybersecurity, as currently practiced, is probably ripe for some nasty lawsuits if a researcher screws up a situation like this.
Does anyone believe that if the registering the DNS address had bricked the NHS systems, the NCSC would've taken the fall?