Almost 2,000 years ago the Roman poet Juvenal was in despair. Muggings in the street, women engaged in traditionally male sport and men marrying each other had convinced him that the social fabric was tearing. He became a brutal critic of all he saw, explaining his acerbic writing thus - “It is difficult not to write satire, when you look at broken society”.

The ancient idea that society is broken finds a spokesman in each generation. David Cameron has decided that in this generation, that spokesman is him. The Leader of the Opposition has claimed repeatedly that we live in a broken society. It is a claim that ought to be resisted.

The recent spate of knife attacks and murders gives strong reasons to share Mr Cameron's concerns about a broken society. The appalling frequency of these crimes, as well as the increasingly young age of the offenders, demonstrates that in too many corners of British life respect for the law and for fellow human beings has disappeared. Knife crime must now be a priority for government, police, parents, schools and for local communities.

There are good political reasons for a party leader seeking power to assert that society is broken. This does not make the observation correct. Crime and social breakdown are perpetual concerns. Anyone who believes modern experience to be novel should try reading Henry Mayhew. Or try reading Charles Dickens. Or look at the engravings of William Hogarth. Or read Tacitus for that matter. That social problems have always existed does not diminish their importance, of course. But it does call into question the role played by recent changes in, for example, family structure or a decline in civility.

Also, claiming that society is broken tells only part of the story. There has never been a time when our society has been richer, lived longer, been more tolerant, guaranteed women greater opportunities, cared better for the sick and disabled or done more to provide education for all.

There are few places in the world that are better to live in than Britain - more law-abiding, more civil and more stable. This is not to deny complacently social difficulties or ignore the many things other countries do better. But Mr Cameron has noted that many people emigrate to Britain. Why does he think that they come?

The biggest problem with the broken society claim is statistical. The singer Lily Allen pleaded last week on her website: “Please can everyone stop stabbing each other in the UK.” Sometimes, when following the news it seems as if everyone is indeed stabbing everyone else. Of course, they are not. The Metropolitan Police recorded 70 knife killings last year: the same as a decade ago.

This is 70 killings too many, but numbers matter. There is a big difference between arguing, as Mr Cameron does, that society is broken, and believing, as we do, that there are broken individuals, families and communities, having an impact on the law-abiding and decent majority. If social breakdown is general, policies are needed to alter behaviour of the average citizen; if the problem is concentrated, so should be resources and attention. Arguing that mainstream society has gone bad demonises the average teenager, the average family, the average public space, the average entrepreneur. Mr Cameron's broken society rhetoric is in danger of leading him astray.

It is good to hear a Tory leader speak of social problems with passion and determination. There is too much crime, too much poverty; and 4.3 million people are claiming out-of-work benefits. Mr Cameron is also innovative and right to argue that social change need not always involve regulation and public spending. There are broken communities that urgently need attention. But Britain is not a broken society.