Not ridicule exactly, but needing proof of which we have none.
To date, not even a fossil of a microbe of alien life has ever been found. We do not have any proof that life exists anywhere else other than Earth, although we really would like to have that proof and it’s likely that life does exist elsewhere.
Proof that life evolved elsewhere than Earth would also be proof that science is right and religion is wrong, but we don’t have the proof. Maybe one day we’ll be able to make up for the fact that Galileo was imprisoned by the Church.