While this could happen anywhere, it happened in Canada where the right to self-defense is going the way of England.
Then don't make any plans in the near future to visit DC, CA, IL or WI, to name a few.
You out to be a Defense Attorney. Because it sounds a bit like a typical gun vs. knife argument. Have you ever seen how much damage can be done by a nut job wielding a knife? I have seen how much damage can be done in just 3 slashes of a knife and I'll tell you that my response to a knife attack is to aim and fire as many times as it takes to put the knife wielder down. The simple fact is that if a major artery is cut during a slashing you will die in about 3 seconds without effective treatment. I should also point out that effective first aid for a slashed corotid artery WILL cause brain damage because to stop the blood loss you also have to stop the blood flow to 1/2 of the brain. So I don't blame those on the bus for running one bit, edged weapons are just as dangerous as bullets.