The official term for people who feel the need/ compulsion to expose themselves to the public is exhibitionist. The fear toward exhibitionists is two-fold. Firstly the fear is that an exhibitionist may expose him or herself to someone who will be negatively affected by their nudity. An example of this victim would be a child. The second fear is that exhibitionism is a gateway to worse sex related crimes. Many violent sex offenders have been exhibitionists too.
There is a great difference between public nudity and indecent exposure. For example a college girl who flashes the people of Bourbon Street on Mardi Gras in New Orleans for some beads will most likely not be prosecuted for indecent exposure. Because of the context of her nudity and, shall we say, the tradition of Mardi Gras, if she is considered an exhibitionist, she will be in the non-threatening category. That's simply public nudity. Inappropriate? Sure. But harmful to others? No.
Now take a middle-aged white guy who throws open his trench coat in the middle of the food court at Tutle Mall. This would be the classic example of indecent exposure, and exhibitionism. Because he exposed himself for no other reason than to shock others and possibly arouse himself, he may be considered a threatening exhibitionist. In the eyes of the law, he may have the potential to become a much greater risk to society.
Obviously there is a lot of grey area between a group of kids who swim naked in a lake and a man who exposes himself to a group of children. The context of the offender's nudity along with his or her motives for exposing themselves will determine if they are dangerous and deserve sentencing. Exhibitionists may expose themselves for many reasons. Some may get sexual arousal from it. Others feel the compulsion to for no other reason than they are psychologically damaged. For example, someone who was a victim of or witness to inappropriate sexual behavior as a kid may become an exhibitionist in their adult life.
The seriousness of indecent exposure comes from the fear that one incident may be a stepping stone to more serious crimes. So the next time you decide to dawn your birthday suit and go for a run through your campus, think about the seriousness of the case. The arresting officer may not think it's as funny as your buddies do.