It's up to the person who advances a thesis to prove it.
Summary
Quotes
“Many orthodox people talk as if it were the job of skeptics to disprove dogmas rather than those who support them to prove them. This is obviously a mistake. If I were to suggest that between the Earth and Mars lies a porcelain teapot in elliptical orbit around the Sun, no one would be able to prove the contrary, provided I took the precaution of pointing out that the teapot is too small to be detected by our most powerful telescopes. But if I were to assert that, since my proposition cannot be disproved, it is intolerable for human reason to doubt it, I would immediately be considered a lunatic. However, if the existence of this teapot were described in ancient books, taught as a sacred truth every Sunday and inculcated in children at school, then any hesitation to believe in its existence would become a sign of eccentricity and would earn the skeptic the care of a psychiatrist in an enlightened age, or of the Inquisitor in more ancient times.”