Reasonable Discussions Aid Equality

Usually, the more people discuss adult relationships that face discrimination, the better, because when people think it though they realize that an adult should be free to share love, sex, residence, and marriage with any and all other consenting adults. Discussions about interracial dating and marriage, same-gender marriage, polyamory, and consanguineous relationships pop up in everything from baby boards to game forums. This discussion took place at thinkatheist.com.

Someone identified as matt clerke got the discussion going...

I allow my mind to wander sometimes (particularly on the bus) and somehow wound up thinking about incest. I get that it's wrong, The thought of being sexual with my brother is definitely not appealing, but I don't get why.
What are some objections to incest?
The two I can think of is genetic diversity is compromised in cases of reproduction from incest, and psychologically it may not be healthy.
The genetics argument is essentially invalid due to the availability of contraception, abortions, and the fact that there are over 7 billion people on the planet.
The psychology argument would be valid if shown to be true, although even then it should be treated as a psychological problem, not a criminal one.

So that touched on Discredited Arguments #18 and 19, more or less.
 

Kris Feenstra had a very reasonable response, and considers Discredited Argument #20...

I am not particularly opposed to consensual incestuous relationships or even marriages. The concerns I have regarding such unions are not unique to incestuous partners, and are not severe enough that I think the practice should be universally condemned. I've never accepted the 'ick' factor to be a legitimate argument against homosexual relationships, so I would be a hypocrite to apply it here.

The concerns I do have:

In the case of inbreeding, the risk of offspring being homozygous recessive for autosomal recessive genetic disorders increases. I don't feel this issue is significant, however, as recessive genetic disorders can be inherited in non-incestuous breeding, and not all incestuous pairs are carrying recessive genetic disorders or are even heterosexual or interested in producing offspring.
Genetic diversity also isn't a huge concern. Genetic diversity is important in the overall population, and allowing incest in a society such as mine is unlikely to have any significant impact. Even given the choice, I think a very marginal minority would choose incest with immediate family or even first cousins or aunts or uncles.
The other concern is the potential for relationships to be formed out of abuse. Members of a family exercise strong influence over each other. A parent, sibling, cousin or, aunt or uncle could have had influence over an individual for their entire lives. In that scenario, it becomes difficult to tell if that individual consents to incest due to their own personal desire, or if it is a matter of coercion. While I have this concern, it is not a unique issue to incest, and unless I can actually demonstrate child abuse, at a certain point we cannot dictate the actions of other adults. For better or worse, we have to trust others to make decisions for themselves.
If that decision happens to be incest? Regardless of my personal feelings about it, that decision does not cause me or society any appreciable harm of which I am aware, so I really don't think it's any o' my damn business.

Based on what I currently know, I cannot object to incest on any grounds that aren't prejudicially discriminatory and hypocritical.

That last line is a good way of saying what I've been showing when it comes to consanguinamory. There is no objection to consanguinamorous relationships that is consistently applied. Usually, it is trying to justify someone's personal disgust. But person A's disgust should not prevent persons B & C from being together.

The more people talk these things over, the more we move towards full marriage equality.