Horse shit if that was the case you would be arguing that family member should be allowed to marry abnormal lifestyle is not liberty it's perversion
There is a clear, concise reason for laws prohibiting marriage between close family members.
It has nothing to do with "perversion" or "lifestyle abnormality", it is simply because incest produces large amounts of birth defects and mutations.
In fact that is the reason for the social taboo in the first place.
If both close family members agreed to be neutered before getting married, then, sure, why not? But unless that is the case, then, no.
Why? Because, like murder, it is harmful to society.
There is nothing you can say that will convince me that letting two people that love each other to marry one another is harmful to society, because it ISN'T harmful to society.
Therefore, denying a certain group the same rights and privileges that any other group can expect from being an American Citizen, is specifically unconstitutional, as per the 14th amendment.
You can go on and on about bestiality and incest all you want, it won't make a whit of difference.
There is no
LEGAL reason to deny the right to enter into a marriage contract to these people.