I think responses to nudity are shaped by the circumstances and frequency of experiences in which nudity is encountered.
For a lot of people encountering others nude is limited to sexual or sensual situations. And the number of nude "others" is relatively few.
Contrast this with the alternative. Here at Noosa Heads is a beach used by unclad people and I have photographed nudes there many times. After seeing thousands of nude people, old, young, fat, thin over many years I can report to you that nudity and sexuality are not inherently linked. Attractive people are attractive whether they are clad or not and jerks are still jerks.
That famous (notorious?) photographer Spencer Tunick who specialises in installations of hundreds or thousands of nude figures in urban settings is trafficking in something but I bet it's not sex or sensuality. I reckon he is using the nude in an unfamiliar setting for its transgressive potential. And good luck to him.
Beyond sexual, sensual, or transgressive I think the power of the nude in visual art is drawn from its capacity to address the human condition. If you want to make a general statement about humanity, good, bad, ugly or beautiful then the nude is an ideal form. The plain nude figure stands outside the context of time, place, and personal identification.
Along with the capacity of the nude to address general themes it also offers an uncomfortable personal reminder that it is basically what we are: skin and bone vulnerable to the terrors and pleasures of everyday existence.