Considering that Elrond is known as Elrond Half-elven, I don't think we are dealing with an unspeakable taboo here. Elf-human relationships are rare, but that is because the immortal vs mortal thing leads to sad endings and it is a sad fate or doom to face that eternal separation. Andreth and Aegnor didn't find a solution to that issue, so they left their relationship behind. Beren and Lúthien DID solve that problem, so hence the Lay. (Well, that, and they successfully stole a silmaril from Morgoth!)
We know that Sam heard the story of Beren One-hand told in the Hall of Fire in Rivendell. Was it the Lay or some other version of the story? That I don't know, but the story is preserved as a tale from the First Age to the end of the Third Age. This is a widely told tale of hope and love.
We know that Sam heard the story of Beren One-hand told in the Hall of Fire in Rivendell. Was it the Lay or some other version of the story? That I don't know, but the story is preserved as a tale from the First Age to the end of the Third Age. This is a widely told tale of hope and love.