Simple materialism, in itself, is patently wrong, simply because we are now aware of all manner of phenomena (even material) that go beyond the reach of the five senses: from radio waves, to cosmic rays, to galaxies beyond the reach of our eyes, to chemical reactions and particle interactions too small to be seen or felt; and that go beyond our current "common sense" notions of reality ("the earth is flat", "the sun goes around the earth", etc.)

Scientific materialism augments materialism in a specific way: reality also includes whatever is directly perceivable via (or directly inferable from) scientific instrumentation used in carefully controlled experiments. Thus even though the immediate senses cannot detect radioactivity, scientific instrumentation can, and thus radioactivity is also considered “real” by scientific materialists. Just so, the reality of galaxies beyond the reach of the visible, or particles or individual molecules, etc. In order for an instrument to classify as “scientific” (and thus be usable for helping to extend the known reality), the instrument must objectify; that is, there is the perceiver, and there is what is perceived via the instrument (whether a telescope or the five senses), and the clear distinction between the two is what allows for “objective” results.

By extension, Freud’s “unconscious”, too, falls within the purview of what scientific materialists (like Freud) consider real. The “tools” used by the psychotherapist include analysis of dreams, association games, recording of the behavior patterns of patients in relation to their mother and father, and to men and women in general, etc. Just as the doorbell ringing commonsensically indicates someone (or something) on the other side of the door, so all the data collected by these psychoanalytic tools suggest that there is something “on the other side” of the conscious driving a human being, apart from their conscious intentions and their autonomic nervous system.

What that “something” — the "unconscious" — is altogether, is another matter.