Why do jurists differentiate in ruling between coitus interruptus (al-azl) and contraception by modern means, even though modern means may achieve benefits that coitus interruptus does not, such as the woman's complete enjoyment?

It is permissible to use modern birth control methods if there is a need for them, and it is a condition for the permissibility of 'azl (coitus interruptus) that the wife agrees. However, birth control should not be continuous, as it contradicts the purpose of increasing progeny. Modern birth control methods may also cause health problems, and some of them necessitate the exposure of 'awrah (private parts) or cause menstrual cycle disturbances.