You have given 1 example of something that you call objectively immoral - and yet there are times in history that rape has been one of the tools of war. All the way back to Genghis Khan, who I have read that genetic testing says that 1-200 are descendants. While I find it abhorrent, as I do murder, slavery, etc., I believe that cultural/religious influences determine "normal"
To use the above nudity example, and expand on it - where is the objective moral status of extra-marital sexual relations, bi-sexual relation, inter-racial marriage, slavery, homosexuality, etc. Many people use historical guidelines, such as the laws of God (Torah, Bible, 10 commandments, Koran/Quron, Vedas, the Tibetan Book of the Dead, Mein Kampf? All have/had many followers.
The earth is the center of the universe, nope the Sun is the center of the universe, and so on - if science can change or recognize new information, then does not the same thing hold true to moral?
Can we judge all people based upon the current moral climate (seems like we do, or at least some of us do).