Why is SEX a taboo in India

SEX, sshhh... dont say it loudly here,chances are u would be labeled as promiscous,immoral by somebody here.Why is sex such a taboo in the country of Vatsayana?Indians cant talk about it openly, somebody going beyond the so called moral boundary is ostracised in the society.
Sex is human being's natural instinct, society makes some rules so as to see things are within a framework.Why such hype and hoopla when two people have sex with mutual consent and without overridingfamilial relationships.I might have sex with my GF or an one night stand with somebody before marriage, I dont think I am doing something wrong.What is most important in a relationship is trust.
People outrightly reject discussing sex in public, now AIDS is spreading like a menace.Even if we keep being hypocrites and let things just run undercover,its gonna be worse one day.