This is discussion archived from a time before the current discussion method was installed.
Why are breasts so taboo?
Seth: Since most of us are clothed all the time we associate not being clothed with the reasons most people take of their clothes - that is sex. So a stigma built around the association, parents teach their children through imitation to consider nudity taboo and it loops.
Big T: Don't forget that genitalia are the most easily injured parts of the human anatomy. This includes the female breasts. We originally covered them up for protection purposes. In earlier times especially, showing these parts was showing yourself to be vulnerable, kind of like when a dog roles over on its back. So we cover them up to avoid implying subservience, revealing them only to our most intimate partners. It's a pretty common cultural theme. It's just that breasts are losing their significance in this aspect.
Here's a counterexample to the girls-never-on-top subtrope: In this QC strip
(Completely NSFW!) we have a girl on top without any naughty bits showing (but with naughty ACTIVITIES fully shown).
