Lela, it may or may not be a bad thing that "some law-abiding citizen on that bridge didn't have a gun". The unbounded optimism of those who think arming more people is the answer to every terrorist event isn't warranted.  In the right hands, guns are very effective.  In the wrong ones, they can pose a greater danger.  Not all armed citizens will carry safely, respond appropriately under stress, be extremely accurate, or instantly identified by police, no matter what they think before something happens. We can't know how many might have been saved, how many bystanders killed by armed citizens trying to shoot the attackers, or how many bystanders and armed citizens killed by police shooting at armed citizens they mistook for terrorists.

It is good the terrorists had knives, not guns, or it would have been even worse.  If it were easier for British citizens to obtain and carry guns, wouldn't it be easier for terrorists to obtain and carry guns, too?