Chrissy Stockton explains the reason on for her article 60 Women On “What I Was Doing When I Was Called A Slut”:
In my experience, the people who call people sluts in an attempt to insult them aren’t even aware of the actual “truth” in their insult. They’re just saying a woman could, possibly have slept around. And that’s bad. I wanted to know what elicited this kind of insult from people so I asked Thought Catalog readers to tell me what they were doing when they were called a slut. Here are the (heartbreaking) responses.
Read a dozen or so and you will see the arbitrariness and absurdity of the accusations. For example:
I was called a slut for not sleeping with a guy. He later corrected himself, though, and told me I was “the opposite of a slut, which is even worse.” At least we got that straightened out.
It seems that the only criterion is that the accused be female. While many Muslims write this off as a non-Muslim problem, throwing around explicit or implicit accusations of fornication has become commonplace amongst many Muslims.
It is unlawful to accuse others of fornication. It is an attack against their reputation and dignity, and it is a declaration that the accused has committed criminal behavior deserving of one of the severest punishments in Islamic law. Something accusers often forget or overlook is that the accusation is itself punishable.
An unproven accusation of fornication is a punishable offense. The accused has a right to seek justice through the court if the accusation is not backed up with testimony from four individuals whose testimony is accepted in court. (The accuser can be among the four.)
An accusation of fornication will often be accompanied by other sins, such saying something about an absent individual that the individual does not want said (غيبة), intentionally spoiling relations between individuals (نميمة), publicizing sin committed in private, exposing secrets, and lying.
Accusing chaste Muslim girls is counted amongst the seven most deadly sins. One of the reasons given for the additional enormity here is that it is virtually impossible to erase doubts raised by the accusation once it has been made. If it is proven to be a complete and utter fiction, even the most respected girl’s reputation will forever be tarnished in the eyes of some members of society. Although are required to ignore all unsubstantiated gossip, how many of us do so all the time, every time?
We have become desensitized to the enormity of the things we say and write about others, especially when joking amongst friends or in our electronic communications. That individuals and society have become desensitized and no longer take umbrage from such attacks on dignity and reputation are not signs of social maturity, but rather evidence of a sickness within our hearts and shortcomings in our practice of Islam.
EDIT 1: The textual basis for punishing unproven accusations of fornication is found in Surat al-Nur: And those who accuse chaste women and then do not produce four witnesses – lash them with eighty lashes and do not accept from them testimony ever after. And those are the defiantly disobedient, Except for those who repent thereafter and reform, for indeed, Allah is Forgiving and Merciful, Q24:4–5.
Given the potential consequences for the accused, it is appropriate that there also be consequences for the accuser.