> When dealing with complex questions of which we have but datapoints, the probability of scenario A vs B moves in a linear scale, not according to arbitrary requirements of "extraordinary evidence".

That may be true, but I the case of interstellar travel, we have mountains of solid evidence to prove it's not possible (essentially all of physics for the last 100 years or so), and some vague claims with 0 evidence claiming it's actually happening. To convince us that all that physics is wrong you have to bring some extraordinary evidence, not claims that you heard someone knows someone who saw something.