Narrowing or widening the range of people with whom one may have sex is ALWAYS political and EUGENIC

The rule against incest is eugenic and moral.  Therefore those who commit incest are being anti-eugenic and immoral.   Eugenics is therefore, wait for it, MORAL.  

Compare the list of people you may not have sex with if you are a man as expressed in Leviticus at http://en.wikipedia.org/wiki/Leviticus_18 with

004.023
YUSUFALI: Prohibited to you (For marriage) are:- Your mothers, daughters, sisters; father's sisters, Mother's sisters; brother's daughters, sister's daughters; foster-mothers (Who gave you suck), foster-sisters; your wives' mothers; your step-daughters under your guardianship, born of your wives to whom ye have gone in,- no prohibition if ye have not gone in;- (Those who have been) wives of your sons proceeding from your loins; and two sisters in wedlock at one and the same time, except for what is past; for Allah is Oft-forgiving, Most Merciful;-
PICKTHAL: Forbidden unto you are your mothers, and your daughters, and your sisters, and your father's sisters, and your mother's sisters, and your brother's daughters and your sister's daughters, and your foster-mothers, and your foster-sisters, and your mothers-in-law, and your step-daughters who are under your protection (born) of your women unto whom ye have gone in - but if ye have not gone in unto them, then it is no sin for you (to marry their daughters) - and the wives of your sons who (spring) from your own loins. And (it is forbidden unto you) that ye should have two sisters together, except what hath already happened (of that nature) in the past. Lo! Allah is ever Forgiving, Merciful.
SHAKIR: Forbidden to you are your mothers and your daughters and your sisters and your paternal aunts and your maternal aunts and brothers' daughters and sisters' daughters and your mothers that have suckled you and your foster-sisters and mothers of your wives and your step-daughters who are in your guardianship, (born) of your wives to whom you have gone in, but if you have not gone in to them, there is no blame on you (in marrying them), and the wives of your sons who are of your own loins and that you should have two sisters together, except what has already passed; surely Allah is Forgiving, Merciful.
004.024
YUSUFALI: Also (prohibited are) women already married, except those whom your right hands possess: Thus hath Allah ordained (Prohibitions) against you: Except for these, all others are lawful, provided ye seek (them in marriage) with gifts from your property,- desiring chastity, not lust, seeing that ye derive benefit from them, give them their dowers (at least) as prescribed; but if, after a dower is prescribed, agree Mutually (to vary it), there is no blame on you, and Allah is All-knowing, All-wise.
PICKTHAL: And all married women (are forbidden unto you) save those (captives) whom your right hands possess. It is a decree of Allah for you. Lawful unto you are all beyond those mentioned, so that ye seek them with your wealth in honest wedlock, not debauchery. And those of whom ye seek content (by marrying them), give unto them their portions as a duty. And there is no sin for you in what ye do by mutual agreement after the duty (hath been done). Lo! Allah is ever Knower, Wise.
SHAKIR: And all married women except those whom your right hands possess (this is) Allah's ordinance to you, and lawful for you are (all women) besides those, provided that you seek (them) with your property, taking (them) in marriage not committing fornication. Then as to those whom you profit by, give them their dowries as appointed; and there is no blame on you about what you mutually agree after what is appointed; surely Allah is Knowing, Wise.

http://en.wikipedia.org/wiki/Lot_(biblical_person)#Lot_and_his_daughters

Hendrik Goltzius' 1616 painting Lot and his daughtersshows Lot being seduced by his two daughters. The fox behind the tree symbolizes female cunning. In the background in front of the burning city is the pillar of salt, Lot's wife.

Which would you say is better drafted and clearer, bearing in mind Leviticus apparently does not prohibit a father from having sex with his daughter?

INCEST PRACTISED BY THE PATRIARCHS OF ISRAEL

Incest amongst the patriarchs includes

1. Abraham's marriage to his half-sister; Sarai[Gen.20:11,12] 
2. the marriage of Abraham's brother, 
3. Nahor, to their niece; Milcah [Gen.11:27-29] 
4. Isaac's marriage to Rebekah, his first cousin, once removed;[Gen.27:42,43;29:10] 
5. Jacob's marriages with two sisters who are his first cousins;[Gen.29:10,Ch.29] and, 
6. in the instance of Moses's parents, a marriage between nephew and aunt (father's sister).[Exod.6:20]