The closest you can get to that in statistics is a strong Bayesian prior agin’ the proposition, which itself has to be justified as more than someone’s whim. And actual evidence in favor of the proposition quickly overwhelms even strong priors to the contrary.
The evidence is either consistent with the hypothesis, inconclusive, or it disproves the hypothesis, regardless of the biases of the reviewer.
Personally, I don’t think there is ET life—at least not complex life. But that doesn’t change what evidence supports and doesn’t support the hypothesis.
I don't know about any "meme." Everything I said is based on experience as a scientist. I have no particular emotional attachment one way or the other to the idea of life existing other than on the Earth, and I think that life has probably evolved elsewhere. That has no bearing on the fact that I am highly skeptical of the claim.
In making the claim that extraterrestrial life has been found, one must absolutely and rigidly disprove the null hypotheses, which are:
--The structures observed are artifacts contained within the sample.
--The sample was contaminated.
It is simple to state these, but incredibly difficult to show them. If the structures are, in fact, microorganisms, then how can it be shown that they are of non-Earth origin? First of all, why they didn't burn up during the meteorite's plunge to Earth? How were they not destroyed by the cosmic radiation, intense cold, and vacuum that characterize space? Even if the structures are the remains of microorganisms, can one be absolutely certain that nothing could crawl inside the rock through microfractures? How can one know that the microtome used to slice the samples didn't drag something onto the pristine slice? Let's say that they are shown to be microorganisms, and their biology is unlike any we are familiar with--well, there are plenty of examples on Earth of organisms that live in extreme environments and have vastly different biologies than those we encounter on a daily basis. And so on.
To control against contamination, the analysis must be conducted in an environment where contamination is not possible--and it's hard to think of a suitable place on Earth. The only way I can see to sufficiently control against the possibility of contamination would be to examine a rock that has never been on Earth, using instrumentation built and operated remotely.
I should also point out that statistics, in this case, is completely irrelevant. In order to run a statistical analysis, you must have something to compare--when speaking of claiming that there are extraterrestrial organisms within a rock, exactly what are you going to compare? What are the appropriate statistical tests?
I don’t disagree with anything you just wrote. But nothing you would like to see is what I would call “extraordinary.” It’s just proving the case in a likely contamination-free way. The claim itself is not characterized as extraordinary. It’s just hard to prove in a rigorous manner.
I thought you were using the phrase in the Carl Sagan sense: “extraordinary claims require extraordinary proof,” which I have always regarded as a bogus concept allowing some self-designated folks to decide that hypotheses they don’t like require a different standard of proof than others they do like.