I have a certain sympathy for the idea - for example, it makes a certain
amount of sense, when a person's date of birth is in dispute, to get a copy
of their birth certificate. However, this isn't foolproof - I remember
someone saying that their birth certificate said "February 30". A good
researcher would have taken the primary source material, and put it in
context. My grandfather's birth certificate said November 11, but he always
said that he was actually born November 1, but that there was a fine for
late registration, so his parents gave a later date. If he was notable
enough to have a Wikipedia article (he isn't) I could have consulted the
original archival material, and said: born [[November 11]], [[1906]]. I
could not have used his story to say: born [[November 1]], despite what his
birth certificate says (as that's OR). A real historian would have taken
the archival material and the anecdote and cross-checked against the story
of their being a fine for late registration, and maybe determined from other
sources whether such practised were commonplace at the time...and then used
that to decide the plausibility of the date of birth (and published it, of
course).
Unpublished primary sources can only be valid sources about the content they
contain ("his birth certificate says..."). In the hands of an amateur, they
really can't be taken to say anything more, we can't evaluate how good the
source is, we can't determine how much weight to give to one source as
opposed to another...