Argument from incredulity
An argument from incredulity is a logical fallacy in which a claim is refuted on the basis that it merely sounds so "incredible" or "unbelievable" that any further evidence for the claim can be simply disregarded.
This is largely a form of emotional argument, combining peer pressure, argument by ridicule, and guilt by association: the refuter has scorned the claimant as ridiculous and unbelievable, and listeners to not want to earn the refuter's scorn as well by seeming to embrace the claim in any way -- even if only to ask to hear the claimant's evidence before deciding.
- RationalWiki sees this as a kind of "appeal to the unimaginative"
- Wikipedia redirects to argument from ignorance
LessWrong Wiki: no equivalent page as of 2010-02-02