MarcK - If you want to talk about knives then you entirely make my case. I'm not an expert on this but isn't it still illegal to sell, carry or use a flick knife? Why? ... because on balance that particular branch of knives is more likely than not to be used in a way that we (the rest of us) don't want it to be used ... because it's dangerous.
Well, in turn, that makes MY case. I disagree that multicopters are
more likely than not to be used in a dangerous way.