There are other countries where you can get guns and where ownership is comparatively high but which don't suffer the same effects as the US. We would have more shootings if guns were widely available, no doubt, but we wouldn't suddenly adopt the entire cultural landscape of the US which makes them so prevalent there.
The 'everyone is the same, everyone would shoot everyone' line of nihilism is just a comfort to gun nuts and right wingers for the most part, it negates any social or cultural problems their society has by making everyone inherently violent. Not to say that anywhere is lovely and pacifist and perfect, but that doesn't make the opposite any more true. Look at the reaction here to Dunblane, our society and culture was disgusted and happy to see change in the laws, for the most part. The fact that we did that while the US is incapable of similar action says something about the differences.