In article , "Richard D.
Saam" writes:

On 10/25/17 1:06 AM, Phillip Helbig (undress to reply) wrote:

"Dark matter" that we just doesn't seem able to see easily. But not
anything exotic. Just that: normal matter.

There are many arguments against this hypothesis, the main ones being
big-bang nucleosynthesis and CMB observations, which both agree that
most of the "missing matter" (i.e. "dark matter" as the term is normally
used) cannot be baryonic.

With what certainty should the 'cannot be' assertion be made.

Relatively high certainty.

In
science, such absolute assertions are very rare.

True. Strictly speaking, there are no absolute certainties. However,
this doesn't mean that anything goes:

http://chem.tufts.edu/answersinscien...ityofwrong.htm

Current big-bang
nucleosynthesis calculations and CMB observation dark matter
correlations should not exclude a complementary dark matter contribution
by some other mechanism.

They exclude, to a high degree of certainty, most of the missing matter
being baryonic. Yes, that might be wrong, but one needs to show that it
is wrong; one can't claim that since there is no absolute certainty, we
might as well assume that an alternative claim---with zero evidence to
support it---is just as good.