Although I've carefully selected images for the homepage (and news posts, when we announce new series of photos) that do not show genitals or nipples, the site overall doesn't truly have a policy about nudes being only "opt in". For example, the critique forums have sketches of nudes posted in them on a nearly daily basis, where any part of the anatomy might be fully visible, and this is fully within our rules. We have advertisements for drawing books in the sidebar that sometimes have nudes of both genders on the covers (though those also follow the no genitals showing rule)
I am sorry if my avoidance of showing genitals and female nipples on the main pages of the site is not enough to make you feel comfortable. However, this is even "cleaner" than many of the images you'll see in an average exhibit of classical paintings, classical statuary or even in our own forums. I don't think we will be changing it at this time.