Why are four witnesses required to prove a sexual crime? Doesn’t this strictness cause increase in such crimes?
Also when a sane person confesses that which is detrimental to himself, that admission with be efficacious that law that kind does not exist here. And if a person himself confesses to have committed adultery then for three times his confession is not accepted and is accepted only after he confesses the fourth time?
Answer: In principal, regarding sexual crimes the laws of Islam have special conditions in which many points are taken into consideration. On one hand there are very severe punishment prescribed for such kind of crimes, which start with lashes and exile and at times ends with capital punishment.
But on the other hand, it had been made difficult the way to prove this sin. For example to prove this sin, the number of witnesses required are double than those required in other types of crimes and any person confessing the crime once is not considered sufficient.
These two views getting reciprocally linked (i.e. the punishment to be severe and strictness in case of proving the sin) gives a special status to these penal laws. And in that way these laws prevent people from perpetrating this type of crime. These laws create psychological barrier in the followers and they keep away from performing such acts. But then too for all practical purposes these laws do not include many people in this punishment.
In other words the real purpose of these types of laws is to prevent people from perpetrating the sin but not to give them death penalty or to finish them off. This effect is created because of the punishment being so severe because the person who commits this sin always every moment has the scene of severe punishment in front of his eyes. And thinks that as a result of some unexpected situation his sin would be proved. On the basis of this he gets frightened and terrified and this fear and apprehension prevents many people from committing such a sin.
Mostly it is seen that for committing a greater sin (e.g. to sell intoxicants and drugs) in special circumstances severe punishments such as death penalty are prescribed. Though these punishments are prescribed in some special situations. But the apprehension of has sufficient effect in the minds of the perpetrators of those sins.
The conclusion of this discussion is that these types of penalties are prescribed to effectively prevent crimes and sins and along with that it does not entangle too many people in its grip. As a result death penalty may be given to only one or a few persons, but it causes great effect in the minds of other potential criminals and this fear is enough that one day they might also get caught.
source : Religious Questions Answered: Logic for Islamic Rules by Ayt. Makarim Shirazi & Ayt. Jafar Subhani