They aren’t stabbing people in bars in London, are they? Just stuff in the street, which is really hard to defend against because if someone is going to stab you they don’t let you know until it is already happening. It isn’t like West Side Story where everyone whips out a knife and dances around. Though it if happened in a bar, I imagine some patrons would at least pick up bar stools for defense after the initial stabbings took place.
And if one is using bombs or vehicles, other than not being in the way, you can’t really defend against that. A guy in NYC off his meds ran over a bunch of people near Times Square.
The fact of the matter is, unless you go through impractical lengths, you can’t ever be safe from a sneak or surprise attack 100% of the time. You can have some level of increased preparedness, but it still isn’t always enough.
