That programme was vulgar. My husband is a martial arts instructor, he is actually one of the UK's leading instructors and runs his own school. I used to to martial arts before we met (in fact thats how we met), and both our kids have done it since they were 5 years old.
The problem is that this programme was not a true portrayal of what happens when young children are allowed to train in a combat sport, the producers of the programme clearly took a handful of pikey scum who fight their kids like dogs, and now lots of parents will think twice before letting their kids participate in something which ought to be encouraged, because they will think all boxing/martial arts schools are like that.
S.J, you mentioned that they were doing thai boxing, the specific type they were doing is called muay thai, and its is barbaric to allow kids to do that. It is most easily described as the original form of kick boxing (if you go to a kickboxing class here, it will likely be a watered down version of muay thai), and it is a full contact sport and completely unsuitable for anyone under the age of 16.
My husband teaches our kids, and above and beyond any fighting techniques they learn, they learn to have respect, they learn how to walk away from a fight, they learn only to engage in combat as a last resort, and they learn that if they ever use their skills to bully or intimidate others they are barred from the class for life. Both of my kids are nearly black belts, and I am very confident that they could handle themselves in trouble, you dont need to encourage aggression for them to do that!!