Bill Maher, during his stand-up routines in the 1980s, let religion off easy.

He only “gently roasted” it, he says in the opening scenes of his new movie, “Religulous” (read: religion+ridiculous). A diffident half-Catholic child growing up, the diffidence stuck with him into maturity and adulthood until nagging questions of doubt became too large to ignore — and that’s when he decided to make this movie. The film crew follows Maher as he travels the world, meeting with Jesus freaks, would-be messiahs, and members of the Trucker’s Chapel in Raleigh, N.C., to discuss his theological doubts. The first 99 minutes of the 101-minute-long film are hilarious.

Throughout “Religulous,” Maher gives followers of every creed a chance to explain their beliefs. His questions are straightforward: “How can you believe in a talking snake?” and “What happened to Jesus between the ages of two and 33?” The interviewees, in their murky and evasive explanations, expose a basic unwillingness to question the texts by which they live. When asked why God permitted the Holocaust to happen, an interviewee just insinuated Maher’s own narrow-mindedness.

Finding no satisfactory answers from the commoners, Maher tries his luck with the experts. Francis Collins, a director of the Human Genome Project, explains that the Bible is accurate because the accounts were practically eyewitness — the writers were only removed by a few generations, and surely nothing was muddied in those intervening decades. A Latino man claiming to be Jesus’ son, with 100,000 followers backing him up, explains his Judgment Day agenda without a trace of irony. An employee of the Genesis Museum points out that Maher can’t understand the way God works because Maher isn’t God.

The “experts” do an adequate enough job making themselves sound stupid, but the stupidity dazzles when tongue-in-cheek subtitles (a reverend: “You can call me doctor”; subtitle: “This man holds no degree”) and rapid-fire editing (aforementioned Latino “Jesus” morphs into Tony Montana chomping on a cigar) are added in. It’s the Borat effect: it would be funny if it were scripted, but because it’s not — these are real people, and they really just said that — it’s laugh-out-loud funny. Add some clever production, and you’ve got yourself a blue-state hit, a self-assuring look at how the other half lives.

The movie’s levity dissipates when Maher begins his own sermon. Shit gets heavy in the last two minutes. When the Doubting Thomas has his doubts confirmed, extrapolation begins. Maher claims that the world’s woes — corruption, raw opportunism by fake priests and fake messiahs, war, September 11 — can all be blamed on religion. Everything that was funny suddenly seems un-funny when the product of closeted thinking is shown to be real, and dangerous. In an odd way, the film’s final few climactic minutes feel like a trailer for some apocalyptic thriller. But then comes the shot of President Bush ’68 pounding his fists and shouting about an ongoing war between good and evil, and we’re reminded that this is real life.