How would contact with intelligent extraterrestrial life affect religion?

[The Mikado]

Go for it.

Does it lead to evangelizing to the aliens? Might they have a faith that gains popularity here? Would the existence of life on other planets cause crises for religions here on Earth or strengthen them?

Can we let the aliens take Jerry Falwell Jr and Franklin Graham home with them? Would we end up regretting that?

[The Mikado]

Taking a stab at my own question:

At least out of the Abrahamic faiths, I think Christianity would be hardest hit.

Islam has a baked in answer: its contention that God sent just about every group prophets at some point to tell them there's only one God and that Muhammad is just the final and greatest of these prophets with the most accurate version. IF an alien species is monotheistic, Muslims can easily go "Sure, God sent them a messenger! They're people of the Book. They just need to hear God's final prophecy..." and proceed from there. It's trickier if aliens believe in multiple gods, have no god, or, worse, have no cultural connection to the concept of God.

Christianity, though, has it tougher. The only Christian group designed with the possibility of aliens in mind are the Mormons, who'd probably be rejoicing at contact, but every other Christian group would really struggle with the idea of intelligent life who have existed for eons with zero chance of salvation. It would be the Native Americans all over again on a much bigger scale.

Aliens would, of course, not really be an issue for religious Jews at all, who have no universalizing inclination and wouldn't particularly care what God or Gods these aliens worship, as it'd have no theological consequence on Judaism if people exist on another planet.

[The Mikado]

Extraterrestrial beings would regard Earth's terrestrial, man-made religions the same way we homo-sapiens regard the hootings and hollerings of wild chimpanzees in the jungle.

Interesting?  Absolutely.  And should be archived and preserved for academic study.  Useful?  Again, absolutely.  Such screeching alerts other members of the tribe to look out for potential predators.  Or where to find the nearest fruit.  

But insightful into the actual workings of the Universe?   Not at all.  And not even close.

So you're suggesting alien evangelists will have more luck spreading their faiths to us? That is a real possibility, too. Easy for a charismatic alien displaying advanced tech to seem like a guru worth following.

I would not rule out conversion the other way, though, or syncretism to form new alien friendly versions of Christianity and Islam and Buddhism, at least. Much like Mormonism is an attempt to update Christianity for the Americas, a new space religion incorporating some alien space God as being the same being actually as God the Father might be a popular new version of Christianity.