Bingowings said:In a universe where Luke and Leia aren't twins it opens up the possibility that the other is Anakin himself.
Which sort of lets Ben and Yoda seem less like patricide keen gits.
They intuitively know that Anakin might turn back at the last minute, if Luke can keep from turning but can't interfere in the process for reasons best known to Jedi.
Huh... I really like that interpretation as well.