The showing of and accentuation breast cleavage goes back far in history. The idea is too show off a woman's beauty. Natural human behavior tends to favor a nude body. However, society and cultural restraints repress that tendency in "polite" society. The presentation of cleavage in fashion is merely an acceptable way of showing off some of the beauty of the female body.
they enjoy being looked at...
Because today society believes that if you have it you should flaunt it. Many of these same women also believe that if a man looks he is a pervert. Men are visual by nature. Modesty can be very attractive, too.
Please back up your China Rape statement. Rape is a violent crime. But, perhaps the Chinese culture views the rape of women who wear western clothing to be just punishment.
The presentation of female breast cleavage is not a resent fashion development. It goes far back in history.
Showing the breasts to advantage has come and gone many times in fashion. The acceptance of the practice comes and goes as well.