One of the best things about Louis Theroux's Weird Weekends (BBC2) is that he almost never looks at the camera. This might sound like a rather meagre foundation on which to build an approving review but, technical detail though it is, it amounts to a matter of morality rather than mere style. It is all too easy for programmes like this - in which a presenter sifts other people's lives and beliefs for the explicit purpose of entertainment - to turn sour and exploitative, however unsympathetic you might find the victims of the exploitation. This is particularly true for Weird Weekends because the show has a kind of fib as its premise - the conceit that the presenter is searching for a personal truth amongst the people he visits. So, in the programme about Born Again Christians, Theroux introduced himself as a doubter ripe for conversion, anxious to know more about the possibilities of eternal salvation. And whatever you think of the cheesy spirituality of the tele-evangelists, it was difficult not to feel at times that he was engaged in a kind of fraudulent exchange, extorting sincere concern in return for a forged need.

Two things prevent this from being distasteful, I think. The first is Theroux's screen character, a studied blend of hesitancy, boldness and candour. His air of disingenuous eagerness clearly lulls some of his subjects into an unwise confidentiality but, when Theroux disagrees with what's just been said, he generally says so to people's faces and does it in a way that allows for an answer; he doesn't wait for the safety of the dubbing suite to get in the last, sarcastic word. The second saving grace is that he doesn't make the camera a co-conspirator in mockery, turning to it for a covert sneer. This requires some resolution, because the lens offers all kinds of temptations to a presenter alone in the wilderness - it allows him to disassociate himself from what he dislikes, to sneakily recover from any humiliations, to ingratiate himself with an audience that may be far more judgmental than he is.

Resisting those temptations involves a certain amount of risk. I'm not going to strike any kind of gallantry medal for Theroux here, because ultimately he remains in control of what happens. But there is a sort of bravery in not taking out insurance against what the viewer might feel. This was most conspicuous in last night's programme about porn, a film which began in frivolous mood as Theroux toured a video warehouse giggling at the range of specialist titles (A Dick Runs Through It; Tongue-Fu; Anal Witness IV) and discussed the hazards of "waiting for wood", but which became more and more sombre as it went on. After visiting a producer whose oeuvre included rape and abduction scenes, Theroux's free-wheeling liberalism hit the buffers - he made his apologies and left. You might argue that there was a duty to moralise here, not just a temptation - but beyond making his own disquiet fairly clear Theroux left the conclusions to you. He made a face as he emerged, it's true, but even here he didn't look directly at the viewer, as if to make sure you hadn't missed his finer feelings. And by including the scene and talking about the dangers of industry (two performers had recently tested positive for Aids) he made sure that the film wasn't flippantly indifferent to its human cost. As in previous programmes, he also built an honest relationship with the people he encountered - particularly JJ, a strange child-man who showed Theroux his collection of Godzilla videos in between penetrating various gum-chewing women and whose shell of insouciance failed to give to Theroux's gentle prising.

There are less formal kinds of boldness too - interviewing a straight man who had just finished shooting a gay sex scene Theroux pressed rather harder on the sensitive issue than most people would have dared; "c'mon, you must have enjoyed it" he exclaimed as the young man made his own exculpating grimaces. Nor would many presenters end such a film with a Polaroid of their naked body being passed around porn professionals for general comment. In that ribald, funny montage Theroux exposed himself to ridicule - which somehow made it all right that he occasionally does the same thing to others.