Lior, I disagree with you. Let's follow up with the pre-marital sex example. I've heard (from Israeli friends and relatives, I myself don't live in Israel) that in a large part of the secular Jewish community in Israel pre-marital sex is accepted, starting about age 17, but under certain conditions: The boy is expected to sleep at the girl's house and the parents, other kids in the house, and the unmarried couple are expected to eat breakfast together in the morning. The unstated cultural message here is, "You can sleep with my daughter, but you'll have to show up for 'inspection' in the morning, willing to look me in the face and prove that you really care about my daughter and aren't just in this for the sex."

Compare that setting with the United States where the general cultural attitude about pre-marital sex is that it is "wrong" but 75% of teens do it. It happens in secret with no parental "inspection" and results in pregnancies and sexually-transmitted diseases at a higher rate than in Israel.

Or how about in traditional societies where there is absolutely no cultural context for pre-marital sex. It breaks every deeply held taboo.

It seems like the question "Is pre-marital sex morally right or wrong" ends up really depending upon a cultural context.