While I agree that the father business was pretty stupid, him marrying his mother is different - he married her as a young woman, whereas as a kid he only knew her after she was a good decade older and had developed worry lines. I mean, how many times have you watched an old movie that stars someone who looks awfully familiar, but you can't... quite... place him, and then the credits roll and HOLY CRAP IT'S SUCH-AND-SUCH! Jack Nicholson is in the original 'Little Shop of Horrors', but I did NOT recognize him at first because he was really young and his face had not acquired the recognizable shape it now has. It's the same general principle - I doubt I would recognize my Mom if I went back in time and met her when she was my age.