Darwinists reject all ideas that contradict their common origin thesis.
But, just to try to remain true to the theory,
couldn’t there be a “common origin” on another planet, “common” being common to that planet,
whilst all life here is “common” to this planet.
I would think that would strengthen the veracity of the theory instead of weaken it.
If they could show that it happened elsewhere, by chance & “deep time”, then that would show that it was possible here as well.