Since women are in mortal danger from muslim men, it makes sense to only allow your daughter to marry a blood relative.
That she is a close blood relative provides some slight protection from the horrific abuse a non-related woman would get.
You might be able to reign in your brother or your cousin as your daughter’s husband, some guy from another village? No way.
There are two main reasons for first-cousin marriage:
1) Bride-price (mahr): the groom is supposed to pay a dowry to the woman, which serves as her alimony in case of divorce. Marry a first cousin, and the money stays in the family.
2) Avoiding dividing clan loyalty: marrying somebody from the same clan ensures that the loyalty of the children is not divided.
Not that it's not just first-cousin marriage, you are supposed to marry your first cousin on your FATHERs side, which concentrates male-oriented recessive genes even further.
If you love your daughter you have very little choice. In islam she is a slave so that daughter you love, you keep her close where you have some say on her treatment (your clan or close family) otherwise if you care nothing for her you marry her outside the clan or family where you have no say on her treatment in a society that has taught their men women are from the devil and a lower life form that you can beat or betray on a whim.
Mulsim incest is a form of love believe it or not. Islam is a sick religion and only leads to evil even when you are trying your best to protect those you love.