As an outsider (a UK person) it's clear the US discussion about guns touches a deep cultural nerve, one that doesn't exist here. It's tied up with the question of individual freedom in a way that isn't the case in the UK.
I think the answer can be found in our history. From the very start colonists needed "protection" from indigenous populations, and it remained that way until the late 1800's. For roughly 250 years those on the fringes of settlements were under constant threat.
My father became interested in our family history a while back. He actually found journals written by distant relatives as they crossed the great plains towards Kansas. There were more than one story of indian attacks. Many of my distant family were killed by indians making the move west. The threat from fellow americans was just as great during both the gold rush and cattle wars of the mid 1800's. There were vast stretches of land with no police, no government presence. You literally settled things yourself, and it didn't always turn out well.
On top of this, you also had immigrants who had emigrated from very tough conditions. A good example is the Scotch-Irish that settled in the hill country of West Virginia. These were people of Scottish descent who had been given land in Ireland in an attempt to gain a foothold in Ireland. They were hated by the Irish for generations and forced out of Ireland. They couldn't go back to Scotland and so they came here. Since then they have always been dispropotionately poor with little promise outside of coal mining. This has led to a community that is fiercly independent. Well, I don't know if independent is the right word here, it's tough to explain.
In the end, the real difference here is the difference in history.