Your opinion only.
There's no proof that one causes the other nor that contraception is the cause of the immorality.
On the contrary, if you consider contraception a sin, then all sin is the symptom of immorality in the heart first.
Contraception does not cause promiscuity.
The desire for promiscuity, which happened first, fueled the demand for the contraceptives.
The availability of contraceptives is the symptom of the problem, not the cause of it. Catholics have it all backwards.
Sin is conceived in the heart before it is born out in the actions.
Except that fear of getting pregnant outside of marriage, used to make a lot of young women remain virgins. Once the pill came along, boom! That healthy fear evaporated.