Of course I think if someone points a gun at you, that's a rather different matter. But we don't have gun culture in the UK, so that isn't really what I was thinking of. Leaving guns (and Batman) aside, I still think it is important to stand up to bullies, even when you know you will lose.
In school, I was bulled around the age of 13 by someone two years above me. I ended up in two fights with this individual - and lost both - but my determination to resist and at least put up a fight meant he moved on to easier targets. I prefered short term pain over meekly enduring long term bullying, and it meant I had some self respect too.