Where genes are flawless, the risks of consanguinity are negligible. This is why Adam and Eve and their offspring had no problem. Adam and Eve's double-helixes, still hot from the celestial forge of the mind of God, were as perfect as human genes can be. While prone from the very first coupling to all the hazards of shuffling and random mutation from replication, the source material they had to start with was so perfect that it would be impossible to find a single maladaptive trait for inbreeding to exacerbate! It would be seven times seventy generations before sufficient imperfections crept into the genome to make an accumulation of maladaptive traits due to excessive dabbling in the same gene pool a risk.
I believe that an enlightened reading of the paleoanthropological evidence will eventually show us that anti-consanguinity taboos arose very far downstream from Eden indeed - and that they arose because people observed the real hazards in action! Those hazards couldn't have shown up In The Beginning. They would only have surfaced after many layers of recombination and mutation had stocked peoples' genes with recessive, maladaptive traits - traits that would only express themselves if both parents carried copies.