Why is it that (american) people can never see breasts, penisis or vagina without going all prudish?
A large number of the people who colonized the lands of what was later "America" were religious extremists called "Puritans"--and they were as fundamentalist and conservative as their name suggests. Even though the mechanisms of the new American government were devised and founded by a bunch of free-thinking, agnostic intellectuals, the Puritan ethos carried strongly through the mainstream of American culture, and continues to reverberate there today.
What most Americans would consider moderate and unremarkable in religious observance would be appalingly overzealous fanaticism to most Northern Europeans. And what the mainstream of America considers politically "liberal" would be considered hard-line conservative in most of the EU, and our "conservatives" would be borderline fascist.
But violence and murder is something you watch without cringing?
America is a relatively young country who was founded during a bloody armed insurrection. This violent revolution is still lionized and romanticized to this very day. Also, much of the American frontier was conquered by outlaws, desperados, and roughnecks, all who frequently came into lethal conflict with both the Mexican conquerors to the south and the aboriginal peoples who wanted the land too. This era of land-grabbing, vigilanteism, and murder has also been sanitized and put on a pedestal as "The Pioneer Spirit of the Old West".
Though most people in America are not violent in the slightest, we still venerate those who are because of our shared history.
Is this tolerance to nudity confined to Europe?
Except for certain tropical tribal cultures who haven't been "contaminated" by Western culture and missionaries, Europe is the place where nudity is most tolerated.
I see nothing wrong with this picture and for what it's worth, this would not be considered risqué in Iceland!
But then again... we sunbathe topless 
Women sometimes sunbathe topless in America too...just not where anyone might accidentally see them doing it.