Fire is good and keeps us warm as long as it is in its place, 'the fire-place!' If you take it to your blankets it will burn a whole house. 

Sex is good as long as it is in it's place, 'Holy Matrimony.' If you take it out to premarital and extramarital engagements the whole family burns.
It has to be in holy matrimony
Apostle Pride Sibiya in his book for the youths, Let's Talk About Sex Babe!