Public nudity in Europe is not a big deal. Very few people walk around nude in public places but should they do it, it is hardly noticed. Nudity is very common at public beaches, even beaches that families with children frequent. Nudity in their TV commercials and other advertising is not uncommon. Click here to read a post on this subject. Europe survived just fine without having a puritan attitude about public nudity.
My wife and I recently went to an museum art exhibition of Lucian Freud paintings. He is considered to be one of the greatest portrait painters of the twentieth century and many of his paintings are of nudes. Most museum paintings of nude subjects avoid the explicit depiction of the male and female genitals. His paintings do not, in fact, they emphasize the sex organs. Click here to see an example. Why is it OK for that painting to appear in public but not OK for a live persons genitals to be visible in public?
One reason for "indecent exposure" laws seems to be a perceived need to protect our children. If a young child has never seen their parents naked, those parents have a problem. Children should know what naked adults look like and it will only be a problem for them if the parent makes it out to be something nasty.
Another reason for "indecent exposure" laws is that there are a lot of adult prudes who will be upset if they see a naked person in public. That is their problem, it is not a problem that should result in the naked person being arrested. I would agree that a line should be drawn if naked people, or clothed people for that matter, engage in a sexual acts in public or act in a way that is intended to purposely arouse.
Many people in America are just too hung up about nudity. Having laws that enforce people to be cover their private parts, and women's breasts, only increases the desire for people to see nudity. What is forbidden is desired. We need to grow up and get over it already!