“... it’s a quick way of setting the characters as off”.
I agree. I remember reading, “The Fall of the House of Usher” (Edgar Allan Poe) and there was incest themes. By themes.. I mean it was suggested. This was definitely a way to set the characters off as not normal.
Similarly, I remember seeing Vincent Price’s “Tomb of Ligeia” as a pre-teen kid and shrugging off the ending as “?”
When I re-watched it years later, and realized the necrophilia theme implied, it totally freaked me out.