I've actually shown that the reasons I've given why consanguineous marriage might be prevented are not the same as the reasons for preventing same sex marriage. I believe I've done so more than once. Apparently you ignored that. Or do you think that same sex marriage was banned anywhere because of the unique relationship between parties which puts one in a position of authority over the other? Do you think that two unrelated homosexuals cannot create a new immediate family because they are already immediate family members?
It might help if you actually read some of the things you comment on.
EDIT : Changed a sentence which sounded nonsensical.
Well, first of all, "marriage" has nothing to do with authority over another, it is the antithesis of that if anything... the joining in union. Second, marriage does not cause or contribute to authority over another which can happen regardless of marriage. Finally, your concerns of parties being influenced by authority are moralistic concerns that frankly are not your business. People exhibit authority over others all across the land and it doesn't seem to bother society one little bit. Some people actually enjoy and prefer being subjected to authority. You come here everyday to be completely owned by me! Who am I to deprive you of that?
I have no idea what kind of point you're making about "creating a new immediate family" when this was never the rationale for allowing gay marriage... then, it was about allowing two people to have the same rights as everyone else. Suddenly it's all about your moral concerns over what it might lead to and what dangers it might cause... all of which are unsubstantiated, speculative and morally subjective reasons you've created in your closed and bigoted mind.
You can pretend that parents don't have a unique position of authority over their children if you like.
I didn't say that marriage causes or contributes to authority of another, I said that the authority a parent has over a child might be considered a reason to prevent their marriage (or sexual/romantic relationship). As with consent, you seem to be willfully ignoring the obvious. There are laws against certain people in positions of authority or influence having romantic relationships, such as a doctor or therapist and patient.
California Law on Psychotherapists-Clients Sex: Direct Quotes From California Laws, offered by Zur Institute, Inc. Would you argue that a parent is in a less influential position over their child? I've already stated on multiple occasions that this argument is less convincing concerning siblings.
When two people get married they are, legally, now immediate family. They get rights as next of kin, decision making, etc.. With marriage between parents and children, or siblings, the couple are already immediate family members and so the creation of a new family does not occur. If the creation of a new family is determined to be intrinsic to marriage, that would prevent immediate family members from marrying.
You have said that the arguments for preventing marriage between close family members are the same as those presented for preventing same sex marriage. I've given you multiple examples in which this is untrue.