well in my opinion, sex is a normal activity. the reason is, with sex the couple realease the hormon to deactive strees hormon in brain, it has been exposed in many literature.
in the other case, all of living thing in the earth need the sex process for reproduction, such as plant, flower etc.
sex is bad when the couple making sex without married because if the girl pragnent it make more problem to the baby, but if having sex after married is normal.
all normal living thing need the sex (my opinion)