Was Religulous an underhanded film?

A recent thread on Pharyngula discussed the Oscars and, somewhat in passing, disappointments over Bill Maher's movie Religulous. The complaint: Overall it's a great poke at religion, but Maher unfairly used some of the same tactics as the dishonest hacks behind Expelled, unfairly eliciting quotes from his targets without first revealing his agenda.

I saw Religulous too, and will humbly suggest that PZ Meyers and many of the commenters on the page are overlooking a key point of the movie.

If I accurately recall my viewing of the film (and I'll happily accept correction), its point wasn't just "religion is bad" or "believers are gullible" or some such Big Broad Theme. Rather, it aimed for a pretty narrow, specific charge: "Many 'believers' don't know what they believe."

The point Maher was after is that many religious believers pound the table with certainty about this Absolute Truth or that, yet when probed, can't say why they believe it, or how to reconcile that belief with apparent contradictions, or what that big Absolute Truth even is! They don't know what they believe because they haven't actually given it any thought, and don't realize (or care!) that they're just mouthing words.

Testing that hypothesis does call for the "ambush" format that Maher arguably employed. Perhaps it would have been sporting and instructive for Maher to make clear that he was representing the side of atheism in his filming, and maybe even to reveal on the spot that he's looking critically at whether believers can articulate what they believe. But to tell interviewees this in advance would be like handing out a take-home test, making it hard to separate those who actually know their beliefs from those who crammed a response.

The point of Religulous was to find out whether theist believers could, on the spot, state what they believe. At least, that's what I took from the film; did anyone else?