'Cause they've already done it, just not with humans
I *meant* with humans. And so did the poster I was replying to, who wondered whether there was a Christian or Hindu officer in all of Starfleet.
There was a Voyager episode where Tom is afraid that B'Elanna's interest in Klingon practices will endanger her, and he says something about "You want to explore your beliefs? Fine, then go to church!" Also, Joseph Sisko once quoted the Bible on DS9 (and I don't mean the Prophet-posing-as-Sisko in 'Far Beyond the Stars').
Of course, anyone who's read the SCE stories knows that there is at least one Jewish Starfleet captain.