As far as I can tell, Michael Shermer has no education in anything scientific.
He was very religious first and later became an atheist.
After earning his M.A. in experimental psychology,
Shermer failed to get into a Ph.D. program anywhere in the country...
..he lost interest in psychology, he switched to history of science..
In 1992 Shermer founded the Skeptics Society..
Such a person is not interested nor educated in astronomy/cosmology at all.
I find that this is usually the case with these kind of people. Whatever education they followed,
they are not really scientists. But they tell other people that their science is false.
They are claiming to know more about something than people that are actually studying it.
The people that are deep in (practical) science themselves do not claim that we know everything.
They may have a formula for most things, but know that they have to investigate a phenomenon
before they can reach a conclusion. They often have interesting tales about strange things
that they do not have an explanation for.
People like Shermer are there to uphold the illusion that science knows everything, so
they keep attacking everything that might show some holes in this illusion.
This behavior divides the scientists that are all genuine interested in the phenomena.
And make it impossible to investigate and test alternative models for the phenomena.
This is pure anti-progress and anti-science.
I personally see these people as mentally ill.
And Shermer clearly shows the behavior of someone who is angry
about the religious environment in which he grew up.
The fundamental religious environment creates traumas, that are later compensated by
adapting belief systems that counter this religious environment.
These kinds of traumas are normal for people who later become "skeptics". Their trauma
prevents them from changing their belief system, because their beliefs "protect" them
against their traumas. They can not see the broader picture. Nor can they introduce or even
work with ideas outside their belief-system.
Next time when he comes, see him as a traumatized person.
Do not talk to him about difficult things, he can not understand them.
Say that you understand his hurt feelings.
You can even give him hugs all the time.
He will quickly leave.