A taboo is derived from context, and context is defined by societal constraint. Society is constantly shaped by history, and history remembers its taboos.
Take the taboo of swearing - it's the usage of words that may offend another person given proper context. Society constrains the words we use so that they may have more than one meaning, and so that they may have stronger meanings given context. These constraints are shaped historically by common conflicts, both internal and external. These conflicts are managed, perpetuated, and maintained by religious or governmental persuasion.
In the case of modern "Western" society, much of our culture is defined by the rise and spread of Christianity. The defining characteristic of the Christian philosophy is to "treat other people as you would have them treat you." Somewhere along the way, people figured out that they don't like having swears used against them, and philosophically were bound to view them as taboo to protect the common trust. No one at the time was able to disagree with this sentiment, as the governmental force of the time consisted of "we'll kill you if you get uppity," so the taboo stood.
It wasn't until the second half of the 20th century that we realized our society is shaped by the people that choose to participate therein, rather than the people that society empowers to protect our culture. I consider myself extremely privileged to be able to swear as I see appropriate, view pornography, and even change my body as I see fit. In recompense for this great honor, I show respect to those we've empowered by not telling them what fucking moronic little asswipes they are.
When it comes to nudity, it's a context thing. I know that nudity isn't equivalent to sex, but the first thought that comes into my head when I see a naked person is either "aw dude, gross" or "I hope she doesn't mind me staring as much as I am." This is because I am culturally and biologically stimulated by the bare figure of other humans (specifically physically attractive ladies.) I believe in our ability to tear down these taboos, but the only way to get rid of them is to remove the base instincts at work.