Skadoosh - Yep, gun laws in the UK are extremely tight and illiberal and the opposite end of the scale from those in the USA. I think we can all agree on that. However, to imply that just because your uncle etc here in England looks down his nose at Americans because of the different ways our societies approach firearms, all British people do, most definitely is 'a bit of a sweeping statement'.
Personally, I feel like the two often peoples miss one another a bit here. British people are often uncomfortable with the American relationship with guns (I for one, am not, but that is because I am a shooter and 'get' guns), because it is completely alien to our own. Some Americans then assume this is some sort of superiority complex and that all British people are ignorant sheeple who think they are better than everyone else while actually living in a little bubble in which they take no personal responsibility for their own personal safety. Guns just have never been ubiquitous in British society, and when legally held firearms were more common, they did not serve as a societal symbol of freedom and responsible individuality and all the things they do for many people in the USA, beyond just being tools.
Our real problem is our insane self defence laws . . . they are quite mad. When it comes down to it, sit down with your average British person and ask how they feel about protecting the people who are important to them and you are going to get the same answers, broadly, as if you are talking to an American. Guns may feature less in the conversation because for better or worse, they are just not a normal thing in British society. We really are not that different.
Sorry, went off on one a bit there and haven't been anywhere near to trying to contribute to the question . . . Tragic gang attacks happen, unfortunately. In any society where it is possible for people to carry guns to protect themselves, it is possible for those 20 scumbag thugs to carry too . . . the outcome might be different, but it might not. Maybe another half a dozen patrons in the pub would have been hit in the crossfire.
I get the argument that that doesn't matter, regardless people should have the chance to protect themselves (because yes, maybe being armed would have saved them).
Still, high cap mags ain't going to save you if you get attacked by a gang who wants to kill you, either they are motivated to do it and fight and kill you anyway, or they flee when you shoot back. I feel that will happen whatever you are armed with (within reason) . . . if they are prepared to do what it takes you die whether you are armed with the j-frame or the glock with the 33rd mag . . . likewise if they are not prepared to do what it takes, either can save your life. You can't argue with numbers, 20 vs 2 is what it is.