Promiscuity is regarded as something which is always wrong, or a sin, because religions teach that sex should only be part of a committed relationship between two people who have deep feelings for each other.
For most of the history of the world, sex has been linked with procreation but the development of successful and widely available contraceptive methods, such as the contraceptive pill, has allowed the act of sex to be divorced from the act of procreation.
The availability of contraception has allowed people to have sex without the prospect of becoming pregnant and it has significantly changed attitudes towards sexual activity.
Religious views on the purpose of sex may have changed as a result of the availability of contraception but promiscuity is still not deemed as acceptable.
Unmarried Christian teenagers and young adults wear a silver ring on their 'wedding finger' to show they will remain chaste until they are married, when married, they will replace the silver ring with a wedding ring.