Before we congratulate our founding editor on his appointment as the nation's chief censor, we should pause to ask what the British Board of Film Classification is actually for. Its title and constitution, as a body set up by the film industry, but with quasi-judicial powers, have a fustiness about them. And sometimes the very idea of censorship can seem somewhat antique.

Most adults will associate the board with the adolescent naughtiness of trying to get into X-rated pictures. For some it might recall the pervasive and sometimes irrational wartime censorship parodied in Catch-22, when Yossarian got the job of blacking out words and phrases in airmen's letters home and spent a whole day unspringing the rhythms in them.

Nowadays censorship seems at once a more serious and a more hopeless task. The range, depravity and accessibility of what is portrayed in moving images, with sound attached (sometimes rather unconvincingly), is indeed alarming. But we should not be too impressed by the vivid tableau, often painted, of the rickety defences of civilised values being swept away by a tide of unstoppable filth, much of it foreign. Satellite broadcasting and the Internet certainly pose new and difficult questions of cross-border policing. But the implied choice thus presented, that we should either abandon censorship or adopt a repressive policy of national autarky, is a false one. Just because break-ins occur, there is no reason to legalise burglary or shoot all burglars.

The only sensible policy is to engage in the argument: to establish clear rules and guidelines, accept that some dirty water will find its way past the defences and to attend always to the causes of things rather than to superficial phenomena. This last is perhaps the most important. We must move the debate on from the pointless attempts to "prove" that screen violence causes real violence. Apparently a Home Office study to be published next month will "demonstrate" a link between violent films and the behaviour of young offenders. Of course there is a link. Not in the simple sense that Dustin Hoffman suggested last year, when he asked if there was a connection between Hollywood's products and the massacres in Dunblane and Tasmania. Sick people will do sick things regardless of whether they have seen The Terminator. But the forms their madness takes will always be shaped by something, be it popular culture, religious visions or media reporting of the actions of other sick people.

Censorship cannot be decided on the basis of what might send deranged people over the brink, but rather as a kind of collective agreement that enables a society to rub along together. It needs to reinforce the rules we set for acceptable behaviour, while allowing the expression and understanding of irregular behaviour. Young offenders may choose to watch films which suggest to them that violence is a good way of resolving disputes or asserting identity. But they will only act on those assumptions if there are no countervailing forces in their families or social groups.

Film-makers and censors need to worry, then, about violence with no moral context, or presented as a source of sexual pleasure. Difficult judgements have to be made, particularly about artistic exploration of the darker side of the human character, but just because they are difficult does not mean they should not be attempted.

Sex, on the whole, should worry the censors less. It too needs to be seen in the context of social rules which enable us to co-exist in mutual respect. If people want to play voyeur on filmed acts of consensual sex, few of us can think of any good reason for preventing them. The only argument against pornography (minus violence) is the continuing concern about the portrayal of women. But that is a matter for social concern, not legal repression.

For these reasons, the system of age certification is a good one. It helps to manage the transition of responsibility from society as a whole to the parent. The primary responsibility for ensuring that children understand and learn from what they watch lies with parents or guardians, and the system provides a useful guide to what sort of thing to expect.

Most importantly, the censors should be confident that they can account for their decisions, because all they are doing is acting as our proxies. One reason for welcoming Andreas Whittam Smith's appointment is that the BBFC has undermined the case for censorship by a series of inconsistent and mistaken rulings in recent years. Jack Straw was right to break the convention that Home Secretaries will rubber-stamp an appointment decided on the basis of Buggin's Turn, and for using his power of veto to install a new broom. We hope and expect that this new broom will bring a coherence and a credibility to the regulation of public taste.