From my understanding, the crime problem has only been around for about a decade or so in Europe. Comparing that to the crime rate in the U.S. which has been around since the 1960s would probably see why the German guy posted with the notion of America being much more dangerous than Germany.
Speaking of crime, I remember one time I went to Baltimore (I was just vacationing in the Eastern U.S., spent about 3 weeks driving from Boston to Orlando- nice drive but too long) and I remember being in the Baltimore Dock or Bay area. Wow, that is a very very nice and safe area. Super clean, ultra modern, what people expect American cities to be like. However, I made the scary decision to explore an area adjacent to this jewel of Baltimore. My God almighty! The buildings looked as if they had been the sight of a war! The people in the streets were very scared of their sorroundings (most were hurrying to get from one place to another), of course I was scared to the bone that I went back to the "nice" part. Then I learned that Baltimore has one of the highest murder rate in the country! Of course, I have seen such thing in other American cities like Philadelphia, New York, Boston, etc., but I'm sure that it's not unique to America. I remember being in Napoli, Italy with a friend of mine and we went into a rundown part of the city. First of all, the streets are soo narrow and the buildings are so grimmy (in that part of town) with lots of clothes hanging, that that view by itself gave me the creeps. I was not aware of any crimes happening there (there probably were some). I just felt like sharing these two things that I have seen on both side of the pond, but for some reason America's ghettos seem more dangerous than any European one. I don't really know why, maybe it's just me! who knows?!