The trouble with that argument is that most of the world does not have and never has needed a Glass-Steagall act. Actually that was one of the justifications for dropping it. Take this to its natural conclusion and it's still a strike against US bankers who apparently need extra supervision or they trash the place.
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1
