An emotional Beckham, 33, said he was just 13 when a mate's brother - a budding footie star who was set to sign for Leyton Orient - was left seriously wounded after he tried to break up a fight.
Speaking at a Government campaign, backed by the FA, dad-of-three Becks hit home the same messages as our Save Our Streets crusade and said: "This has to stop".
Becks said: "He was walking down the street one afternoon and he saw a fight break out over the other side of the road. He went over to help and ended up getting stabbed in the back and was paralysed.
"No one wants to see the devastation that I saw my friend and his family go through.
"As a parent you don't expect to pack your kids off to school in the morning and never see them again.
"So it's something that's very important that us as footballers and us as a team can get involved in, being in our position.
Flanked by England teammates David James, 38, and Rio Ferdinand, 29, as well as Home Secretary Jacqui Smith, the LA Galaxy ace called on youngsters to think about what they are doing before getting involved in violence.
The players will turn out against the Czech Republic tomorrow in a friendly at Wembley.
Now long-time anti-knife campaigner Ferdinand has said enough is enough.
The Peckham-born Man Utd defender helped set up the Damilola Taylor Trust in 2000 after the 10-year-old schoolboy was left in cold blood on a South London stairwell after being fatally stabbed.
He said: "In the past maybe there wasn't a strong enough deterrent for carrying knives.
"If you go to prison now, it will be a step in the right direction.
"People need to know it is not always the person intending to hurt someone who gets injured. People carrying the knives also get hurt.
"Communities and youth centres also need to play a bigger part.
"Boredom can set in a lot of times, there is a lot of peer pressure and then something happens that everyone regrets."
The Home Secretary added: "I'm delighted the FA and the England team are supporting our campaign warning youngsters of the severe consequences of knife crime. You can only solve this by working together. The England players are role models for this generation and I hope their messages have a positive impact."