The matter of pet scientific theories and personal biographies have
something in common: we can't verify them because the only material we
can find on them is written by the author.
So I suggest that we focus on this angle. We already have a policy that
"Wikipedia is not a primary source".
This provides sufficient justification for not having these types of
articles in WP.
We should perhaps try to come up with loose guidelines as to how many
primary sources we require.