When claim/explanation X is fantastical (extraordinary), when there are other claims or competing explanations that contradict X, and when there is no good evidence to support X, then obviously it is insane to believe that X is true and live our lives and perceive reality accordingly. The rational reaction is skepticism and suspension of belief. And because the claim is extraordinary--not a mundane one--the evidential support necessary before we begin believing must proportionally be extraordinary in strength and quality (e.g., we demand much more and much better evidence when someone claims to have $10 million in cash than when he claims to have $10,000.).
Mike claims that the Malarkians visited the earth 4 billion years ago and seeded the planet with DNA to get life going on our planet. Like a Johnny Appleseed the Malarkians are a race of beings who go around the universe sprinkling DNA on planets they know are fertile enough to support and beget life. But that is how far they go. They don't stay around to tend the garden so to speak. They let life fend for itself.
Bob, meanwhile, claims that it was the Bunkos who had brought life to earth. They accomplished this by shipping in the simplest forms of life first, then on succeeding voyages they ferried in more and more complex creatures, culminating in the shipment of the species of the genus we call Homo. (Bob claims that stories of UFOs and aliens in modern times could mean Bunkos have returned yet again.)
Dan, on the other hand, adamantly maintains that it was the Dorkians who had created life on earth. Dorkians have unimaginable telekinetic powers and were able to create and assemble the various species by thought alone without ever leaving their home planet far away in another galaxy.
Which genesis story should we believe in then? In order to find out let's peruse them: Neither Mike, Bob, Dan nor anyone else has any evidence for the existence of Malarkians, Bunkos, or Dorkians. And for that matter, neither is there evidence for space analogues of Noah's ark and the phenomenon of telekinesis). Furthermore, the above claims are contradictory--these claims/hypotheses can't all be true simultaneously. Finally, they all postulate and allude to novel entities--Malarkians, Bunkos, Dorkians. This makes them unparsimonious compared to, for example, abiogenesis hypotheses (that given the conditions on earth billions of years ago life on earth originated from nonlife, via simpler chemicals and processes).
Because of these the rational thing to do is to suspend belief in all of the above explanations until there is strong evidence for one of them. We must also keep in mind that these three do not exhaust the set of possible (and plausible) explanations. Indeed some other explanation may supersede the above and gain credence because a plethora of evidence from various disciplines support it, because it has much predictive power not just explanatory power of past events, and because it is more parsimonious.
Now when we apply the above criteria to supernaturalism (supernatural claims/explanations) we discover that it fares worse than the above extraterrestrial claims because while extraterrestrial life is a purely natural phenomenon the supernatural entails postulating a far more novel phenomenon, one that supposedly is outside the universe and outside the compass of what we can observe, investigate, and test (if we could observe and test it, it would be deemed a natural phenomenon).
1. Hindus, Judeo-Christians, Muslims, and all supernaturalists do not have a shred of evidence for the existence of their respective deities and cast of characters in the supposed supernatural realm, nor do they have evidence for their other supernatural claims and explanations.
2. The supernatural is an extraordinary claim; it is fantastical in nature; it is redolent of Tolkien and Rowling novels.
3. Their claims do not cohere with one another (e.g. The Hindu gods are nowhere like the Christian deity and Hindu cosmology is cyclical rather than linear; the Judeo-Christian deity commands Christians not to worship any other deity, while the Muslim deity forbids Muslims to convert to another religion*). They can't all be simultaneously true. Given contradictory claims some or all of them must be false.
4. Thousands of years have elapsed and not one of their supernatural claims has been evinced to be true.
5. Explanations that assume a new realm and new beings--a preternatural universe, preternatural beings, and forces/processes beyond the natural--are quite unparsimonious.
The rational reaction then is to be skeptical of supernatural claims/explanations, to not believe in any of them until strong evidence is presented.
Vis-a-vis the criterion of parsimony, natural explanations will always be superior to supernatural explanations because the latter always entails allusion to and assumption of phenomena outside the universe. All other things equal, simpler explanations--ones that do not assume new, unknown entities--are favored.
* In Deuteronomy 13:6-10 the Judeo-Christian deity commands his people to kill--to stone to death--their kith or kin if s/he entices them to join another religion (perhaps persuading them by extolling how much better the other religion is). See also Deut. 13:12-15. Meanwhile, the Muslim hadith tersely and plainly commands, "Whoever changes his religion, kill him." (Sam Harris, The End of Faith, New York: W.W. Norton, 2005, p. 115). Muslim apostates are to be summarily liquidated. Read about the Afghan Muslim apostate who faces the threat of death penalty.