I've read comments on the net from folks claiming to be atheists and they can be as militant as the most determined Southern Baptist or Pentecostal. So, it would probably best to leave the atheists at home too. I have to admire an honest agnostic like Bart Ehrman. He's done the reading. He's done the teaching. He's done the thinking. And at this point he's just not sure what he's willing to swear to right now. At least someone with that mind set might be willing to take the time to find out where the alien is coming from.
As I mentioned before I ran across a review of Pale Blue Dot that took Sagan to task for suggesting that we could terraform other worlds as long as that didn't have native life forms. Presumptuous. Arrogant. And so on and so forth. I noticed that the reviewer (apparently Catholic) had no problem with sending communities of colonizers with both lay and clerical members. And we know how well that worked here on the home planet. Just ask the spirits of the exterminated tribes what happened when the bearers of the cross or crescent came to their homelands.