Absolutely made me remember: "I don't know who you are. I don't know what you want. If you are looking for ransom I can tell you I don't have money, but what I do have are a very particular set of skills. Skills I have acquired over a very long career. Skills that make me a nightmare for people like you. If you let my daughter go now that'll be the end of it. I will not look for you, I will not pursue you, but if you don't, I will look for you, I will find you and I will kill you."
I mean it's better than nothing IF you are in a situation like that. Most countries don't allow any kind of self-defense gear like weapons or mace, especially not when going on an airplane. This is something robbers will know, plus you will stand out as a visitor - stand out as an international traveler (so not poor), unfamiliar with the surroundings, and likely without any kind of self defense.
Mind you, if you do get robbed, it's probably best to give up the goods anyway instead of try and fight. Make sure your passport is safe (keep it somewhere else than your wallet / phone / valuables) and you should be all right.