Yours is a common argument, but isn't it functionally equivalent to, say, breaking up GS into two firms, each of which would be able to do one of the roles? If

Yours is a common argument, but isn't it functionally equivalent to, say, breaking up GS into two firms, each of which would be able to do one of the roles? If so, isn't this primarily about economies of scale? Since the only reason both roles take place within one firm today are because there are efficiencies associated with the ancillary services (and perhaps capital requirements) that give a conglomerate iBank an advantage over two smaller firms. ??