Certainly the recent spate of fatal stabbings in London is an indication of just how prevalent knife crime has become: knives have killed 20 London teenagers so far this year. These figures fly in the face of official statistics that suggest that all crime, including the violent sort, is going down. But more importantly, the stabbings highlight the fact that we are now at a crossroads in terms of how we approach such social problems, especially among young people.

We can either try more of the same of what has failed already - the patronising liberal approach of excuses, embraced by almost the entire corps of professionals dealing with young people - or else take a tougher approach that forces people to take responsibility for their own lives. And it is a tragedy that one of the standard-bearers in this city for the latter approach is Ray Lewis.

I know Ray and I know his Eastside Young Leaders' Academy. He is a man who understands the situation our young people are in - and has clear solutions. One cannot help but be impressed by the transformations that he achieves in young men written off by almost the whole of the rest of society - and certainly by the liberal establishment. It uses military-style discipline and drilling as well as after-school tutorial help, mentoring, community work and holiday programmes. And it aims to get three-quarters of its boys into university.

Whatever errors Ray may have made in his short-lived political career as Boris Johnson's Deputy Mayor for young people, I know this: in the long term we will all suffer if his approach is discredited.

Labour figures have crowed over Ray's downfall - but what is their alternative to his approach? At the weekend, Jacqui Smith, the Home Secretary, said she will introduce new measures such as making young people visit stabbing victims in hospital and meet their families. Does she really expect kids who have been watching extreme violence in films and on the internet since the age of 13 to be shocked by that?

We don't need such gimmicks. There are already plenty of laws in place to deal with these crimes. What we need is a change in attitude as to how we raise our children. Ray Lewis understands that.

For so long now the Government, the professionals in schools, the youth justice system and elsewhere, and liberal commentators, have been providing excuses for bad behaviour and the violent crime it leads to. Meanwhile, we've got the schools secretary, Ed Balls, attacking faith schools - which for some inner-city youngsters provide some of the only discipline they ever see.

I know what it's like to come from a poor background, growing up in a tough area, north Kensington. But it's no excuse. Much has been made of the link between poverty and crime: it's often used as an excuse for seriously anti-social behaviour. But few of these stabbings are motivated by robbery. They are much more about bullying and simply inflicting injuries upon others to exert power.

Another commonly held belief is that young people who get involved in knife crime have low self-esteem. I've been a youth worker for more than 19 years and I've found that many of those involved in these types of crimes actually have a very high opinion of themselves - this is part of what allows them to justify their actions to themselves.

Indeed, a fairly small group of individuals who feel this way has a massive effect on those around them: many aspects of their extreme behaviour become acceptable among their peers.

The first thing to understand about knife crime is the fact that it's not about knives. There have always been many knives on our streets - it's just that people weren't nearly so ready to use them before. That they are now has much more to do with the way we raise our children: about their morality and about how safe we make them feel on our streets.

We, as adults, parents and families, need to ensure that our children know that there is always a choice about how they behave. It starts in the home. We have to see child-rearing as our responsibility: we cannot expect the police and teachers simply to pick up where we have failed. We have to set boundaries and challenge bad behaviour - and support those institutions that do so. And we - the adult population as a whole - also have to make our children feel safe, by giving them the kind of proactive police and justice system they need and we need too.

Anyone who lets their children spend more time watching television, playing computer games or on the street rather than with a parent or their family is not taking the responsibilities of parenthood remotely seriously. The decreasing amount of time we spend with them shows a lack of respect for them, as does allowing them exposure to extreme violent and sexual images in computer games, on the net, in films and on television from a young age. All this helps cement the separation of them from us, and the formation of their own moral code.

The difference in Ray Lewis's approach is to provide clear boundaries and leadership to the young people in his charge - not the wishy-washy apologies for bad behaviour of those who see all young people from anything other than a middle-class background as victims. If you treat people as victims it becomes a self-fulfilling prophecy. For a whole generation of children whose families are trapped on benefits, it removes their hope before they've even started, making them feel the victims of forces beyond their control - and removing any sense of responsibility for their own behaviour.

Dealing with the knife crime epidemic is going to be a long, bumpy ride. In the short term, we need to improve the safety of our streets, thus making our children feel safer and less inclined to carry knives. Those caught carrying a blade in public without a proper excuse should expect to go to jail, not just get a caution, as most do at present.

But in the longer term, it's about a more ideological choice. And in that respect we can learn a lot from Ray Lewis, in or out of City Hall. We need to teach children self-discipline and respect for themselves and others. We need to provide them all with opportunities. We need to stop making excuses for them. And until we do so, we will continue to be shocked by these terrible crimes.

• Shaun Bailey is Conservative Party parliamentary candidate for Hammersmith.

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