Why Is Sex Immoral?

All in all.

The desire to have sex must never exceed the need to make wise decisions in life.

Peace out

Sex in itself is not immoral.  It is the context in which it occurs that may be immoral.

Infidelity/Fonication/Adultery
Sexual assaults on males and females--Underage/Molestations
Polygamy/multi sexual partners

If used in the right context--nothing immoral about sex at all.---Depending on your religion.