I'll acknowledge that my experience is limited, but as a former accountant in a small accountancy/auditing practice (less than 20 employees) that had to compete with dozens of other similarly sized practices in the same geographic area, all of whom managed to not be corrupt... it seems to me there's a solid argument for breaking up the Big Four into smaller auditing companies. And if that means there are corporations who are too large to be audited... well clearly those corporations are too large and would also benefit from being broken up.