You gotta think of it this way, though. First, they kept making the argument that if the earth was like a mile off its orbit then life as we know it would seize to exist. Then they made the argument that planets are a rare thing and that our solar system might be the only one in the cosmos with planets. And then when they found extrasolar planets, they made the argument that rocky planets in habitable zones are extremely rare such that earth could have only existed because god created it this way. You see where I'm going with this? They keep moving their goal post. Now that we've found hundreds of planets in habitable zones, I'm just hoping that they could finally shut the hell up.
I'm not 100% sure who you mean by they but if you are referring to Christians I can't see the connection. Whether the Christian faith represents reality or not has nothing whatsoever to do with life on other planets.
I just don't see why anyone's belief in the idea that there is life on other planets has any connection with the Christian faith. I would assume that a Christian would be just as likely as anyone else to believe that there is life elsewhere, although a Christian would assume that life on other planets would be the creation of the same god that created us.