Why does The Bible not say that you cannot be in love with your friends and family members? / Is there a difference between love and sex? /.
There are different types of love., and sex is physical union that can be based on love or based only on lust, or both.
It can be that sexual intimacy is between 2 who love, but there are scriptural rules regarding sexual union not being allowed outside of marriage.
The BODY is a very interesting situation, as it can become passionately inflamed, and once it does the mind will not care about morality.
The imagination within us, if not controlled and contained, is a literal live wire on fire, and does not case about morality or consequence, nor heed conscience. This is why we have to take control of our thought life, or it will take control of us, and never for good.
INcest and pedophilia and sex crimes in general are related to the conscience in a person not in control of their morality or behavior because LUST has taken over the mind and desires beyond the point of no return.