Well, with guns there is a sort of vicious circle going on in the US. As you said, its true that criminals DO have guns in Europe, and its not so difficult to buy one on the black market... But criminals (mostly drug dealers, "mafia" members, etc.) just do not carry guns around, they have them to kill other criminals or defend themselves from other criminals (or the police, if needed). In Europe, Spain, etc. you won't read about a random guy killed in his house (or on the street) because a robbery/assault, you will read about a drug dealer being executed by another drug dealer (just happened not so long ago near my house), russian gang members killing each other, etc... And still this happens just a few dozens times per year in countries with +50 million inhabitants, and nobody in my country feels unsafe or with the need to carry a gun.
Around where I live, you don't read about anyone being murdered in their house or on the street. We had a few burglaries over the years (I think two in the last 10), and the shop down the street had armed robberies maybe three times, with no one shot or hurt, but we haven't had a murder in as long as I remember. I think most people here don't have guns either. We are safe not because we don't have guns, but because we live outside the city, in a fairly affluent neighborhood. Just maybe ten miles away, in the urban area, news of shootings and murders is a bit common. I don't know if they have more guns. I suspect not many more, since the same "you are not allowed to carry a gun at all" laws apply to them, too, but criminals still get guns, and violence is still somewhat common.
So, it's really the area, the culture, and the people. You're making the same mistake as FirstAscent, thinking that your country has fewer murders because of a lack of guns. It's not. It's because of your culture, society, and people. We just happen to have a lot of areas in US with a lot of bad people.
The point is that the less violent is a society, the better for everybody - and the US is a very violent society.
I think what you and many others on here are missing is that you think of US as one country with one type of people. US is huge, spanning from Portugal to West Russia, and from Poland to Greece. And it's full of many different cultures. Some are shit, some are violent, some are stupid rednecks, some are high class Victorian, some are industrial, some are high tech or Neapolitan, some are metropolis urban, and some are Robo Cop dystopean. We have English, French, Spanish, Italian, and Russian all mingling all over the place, trying to live together. So, when you think "US is a violent culture, because they like guns and have a cowboy mentality," you may be only thinking about one tiny part of US, or even be conflating a bunch of cultures together.