I'm not sure how I'm supposed to supply my premises. Ex: "P1: Marriage is granted to consenting adults. P2: Adults who are siblings can consent to marriage. Therefore: Adult siblings should be able to marry." Do I put each premise in a separate "Because" block? Do I put complete argument in 1 block?
If done to enough extent, it could cause a genetic bottleneck, which contradicts our social and genetical imperative. So from a biological perspective it is counter intuitive, but from an ethical or moral stand point, I see no problem with it.
Hm. I didn't mean for this to be published yet. I was going to fill out an entire tree with the arguments for and against, and also try and figure out how arguman intends me to create collections of premises. Oh well. Let it ride
You are assuming the State should be involved in marriage at all. A better solution would the that two (or more) consenting adults can form a contractual household with a single 'taxing' identifier. The "marriage" aspect should remain a non-civil (personal or religious) matter entirely.
The premise assumes that marriage should have a legal status. One can argue that marriage, as a pledge, or as a contract between two equal and consenting parties, is outside the realm of what the law is supposed to regulate.