This is actually great in demonstrating the human rights. People has the right to bear their bodies for a great cause, such as arts, education, and awareness (i.e. demonstration by PETA).
Don't get it wrong, not promoting pornography here, but doing nude photo shoots in concerted, planned, orderly and controlled fashion are of nothing to worry about. Spencer Tunick and his team did well here.
Don't drag politics and religions into this topic. Don't do it yourselves if your believes against it and learned Muslims at large know the boundary, but embrace the basic rights of humans. Many of the world renowned artworks involves some form of nudity, especially those from Greek civilisation.
Of course, we are not to expose our bodies just for the sake of exposing, or walk around the streets without proper clothings as you like - that is in violations of laws and the civilisation.
Additionally, we ought not look at our bodies as shameful piece of items - which should be an artful creation of god(s) [WHOever your god(s) is/are].
Read the following news article for more info: