If you knew anything about human genetics, you would know that close relatives are rarely attracted to each other. That is a protection that evolved to prevent too similar genes from being combined. The incest that happens today is simply one person forcing their power over another.
That being said, if someone actually gets to the age of consent and really wants to marry a parent, then genetic counseling would prevent it from being dangerous. Now, go run around your school and ask how many of the kids there would like to marry a parent. LOL What any kid wants to do is GET AWAY from their parents!