Come on, BB. Hardly anyone would make that claim. Well, maybe some hard-core devotee of "materialism" or something. But from the scientific point of view -- which is not congruent with philosophical materialsm -- items which can't be observed or tested simply aren't subjects for scientific investigation. Which is a whole lot different from saying that such things don't exist.
We were speaking of Truth, PatrickHenry, not scientific knowledge per se. Many people do not make a distinction between the two, literally believing that if science can't demonstrate it, then it is something that need not concern us. You know there are many people like that just as well as I do. Including philosophical materialists, who ape the methods of science, applying them to their own areas of inquiry whether or not they are the proper tools for the job.