Is self defense considered a no-no, or just self defense with a weapon? Are you allowed to meet violence against you with equivalent force on the your (the victims) side?
The "Reasonable force" doctrine means you can use a weapon, and use more force than your attacker has, if a reasonable person would have. It's understood that the reasonable person would be scared and a bit panicked; "reasonable" doesn't mean some unrealistic level of rationality.
The bit you may find hard to understand is that although self-defence is OK, preparing for it usually isn't. If you happened to have a knife by your bedside for peeling fruit, you could use that as a weapon, but keeping a knife by your bedside specifically to use as a weapon against intruders wouldn't be. And that's what this amnesty is about. Youths carrying knives intending to use them as weapons.
The only logical solution is to get rid of all those tools - no screw drivers, nails, scissors, pencils, pens, etc.
Knives as tools are not illegal in the UK. I carry more than one, for example, and of course cooks' knives are fine in a kitchen. The amnesty is aimed at knives that have no real purpose as tools.