“He would not allow Halacha l’maaseh to develop in such a way that one would be liable to be punished for believing something which is true”
That’s assuming that there can be a psak halacha l’maaseh.
But for the moment if I grant that there can be a psak, what happened before the psak was accepted? If you say that everyone was excused then there was no need for a psak. Besides it doesn’t really make too much sense because according to this we are worse off now that there is a psak – before the psak everyone could just believe what they thought but now they would be apikorsim. Also it sounds as if you are saying that it would be impossible for the wrong psak to be accepted. Do you know of any source for such an idea? And if people had tried to make the opposite psak become accepted what would happen?