Why Americans take sex as the bottom line for marriage? Answer is same as what Chinese care: responsibility責任感People need to take responsibility for the family they build and the people they love and loved by. If one conduct out of marriage sex, this shows:You do not love yourself by risking your own life on sex transmitted diseases, such as AIDS, hepatitis C etc.You are not loving your children by risking them their father’s lifeYou do not love your wife by cheating and put her in risk of infectious sex transmitted diseases.