since you claim you can’t measure this even as a thought experiment, there’s nothing to discus
You're going to have to lose the LessWrongy superstition that you have to be able to assign numbers to something for it to be meaningful. Sometimes when talking about this big, messy, complicated world, your error bars are so large that assigning any number at all would be meaningless and lead to error. That doesn't mean you can't talk qualitatively about what you do know or believe.
Part of a balanced breakfast!