Other than admitting that he made the movie HE wanted, he doesn't admit any of it's flaws.
Since "flaws" in the realm of film (they are not automobiles) are wholly subjective, obviously Singer won't "admit" to any flaws because he doesn't see it. Because he made the film he wanted to make.
"If you want to save yourself the ticket price, go into the kitchen, cue up a male choir singing the music of hell, and get a kid to start banging pots and pans together. Then close your eyes and use your imagination." - Roger Ebert on Revenge of the Fallen.