I believe that consenting incestual love between siblings should be legal.
1. It is not up to the courts to decide what consenting adults are allowed to do.
2. "The fundamental right of adult siblings to sexual self-determination" overrides all other moral considerations, including "the abstract idea of protection of the family."
3. The sexual libertarian principles that justify same-sex marriage logically apply to incestuous relationships as well.
4. Justifying activity A with reference to principle X opens the door to justifying activities B, C, and D, if they too, conform principle X.
5. See Lawrence v. Texas
6. While there's about a 2% risk of birth defects in the general population, first-cousin children have about a 4% chance.