No..I don't accept that at all. As I said initially, statements proven to be true are unfalsifiable. Once I am measured to be 6 ft tall, the claim that I am 6 ft tall is unfalsifiable.
I strongly disagree. If it's true that if you are indeed six feet tall, then no accurate measurement will disagree. But the
possibility of those measurements disagreeing remains. That's what falsifiability is concerned with.
Imagine me hypothesizing that 'God is omnipotent' and can do anything. So any state of affairs would seemingly be consistent with the existence of an omnipotent God. No possible state of affairs and no possible observation would be inconsistent with the hypothesis. That's what it means to be 'unfalsifiable'. In the example of measuring your height at six feet, there are all kinds of possible observations that would be inconsistent with you being that height,
even if none of them are observed in actual fact. We still know what it would mean for you to be measured at something other than six feet and what kind of observation it would take to show that.
This conjecture about someone still being able to measure me and prove I'm not 6 ft tall doesn't mean the fact is falsifiable. It hinges on an entirely hypothetical situation that doesn't exist---IF I weren't 6 ft, then it could be falsified by someone else measuring. But there is no such "if" about the fact of me being 6 ft tall. That's what makes my being 6 ft tall a fact.
The possibility of detecting if you
weren't six feet tall is what falsifiability is concerned with. 'Falsifiable' is not synonymous with 'false' such that truth excludes it. It means not only
could have been false (which introduces probabilistic considerations since now we are talking about possibilities) but also that
there is some way of detecting if it is false.
As I have shown, anytime science makes an existential claim, say that neutrinos exist, would therefore be unfalsifiable.
I think that you made an excellent point that rocked your opponents back on their heels. But it's important to notice that not all existential claims are the same.
There's a big logical difference between saying 'This particular observation was an observation of a neutrino' and the more airy and open-ended 'neutrinos exist'. They look very different when we try to falsify them. We can assign a constant to a particular observation (call it a) and say 'aN' (where N means 'is a neutrino'). Falsifying it gives us (~aN). No problem.
Falsifying 'Neutrinos exist' produces 'neutrinos don't exist'. In predicate logic that's a universal statement 'For all x, ~xN' (where 'xN' means 'x is a neutrino'). That lands us in precisely the problem that Popper was originally trying to extract us from, the problem of induction. We can examine x's, one after another (nope, not a neutrino) and never be sure that the next x we examine won't be the neutrino that we are looking for. Popper himself recognized this difficulty.
But saying 'this particular observation was an observation of a neutrino' doesn't fall prey to that particular difficulty. We are just applying some defining standard for neutrinos (which will probably be some universally quantified 'for all x' theoretical statement that itself falls prey to the problem hat induction creates for the positivists' verification principle) and are determining whether the observation in question meets that standard. If it does, we are justified in saying that what we just observed was a neutrino (according to that standard). And once we have an example of a neutrino being observed, then the universal statement 'neutrinos exist' has been verified as well, since all it takes for it to be true is one neutrino.
Popper was arguing against the positivists' verification principle that insisted that in order to be scientific (or even meaningful in the more extreme versions) a statement had to be empirically verifiable. He proposed his 'falsifiability criterion' because the problem of induction renders verification of universal statements from individual confirming instances problematic. What he was thinking about were the general principles of physics, its so-called 'laws'. His observation was that falsifying universal statements with individual disconfirming instances doesn't encounter the difficulty that verifying them does. No amount of positive verification will ever logically prove a universal law true, but only one disconfirming observation can prove it false.
Confirming individual observations doesn't fall prey to the problem of induction (assuming the truth of the theoretical principles, which is itself problematic as we've just seen) since it merely consists of determining whether an observation conforms to a larger defining class. If it does, then just a single observation of x will serve to logically verify 'x's exist'.
So I'd say that falsification isn't a "scientific method" shibboleth. It isn't satisfactory, in and of itself, to be a demarcation criterion between 'science' and 'pseudoscience'. It probably needs to be understood in conjunction with verification. If a statement is subject to empirical verification, then we should recognize that statement as scientific (or potentially scientific) even if it isn't falsifiable. ('Neutrinos exist' might arguably be an example of that. All it takes to verify it is observing a single neutrino.)
My belief is that all of this stuff is more complicated and subtle than the simplistic "scientific method" version that kids get in high school would lead them to believe.