The argument is as follows:
Only an external agency should conduct an audit to establish that we are a quality company.
In some sectors (e.g. health) they argue that such accreditation will ensure compatibility and comparability.
Leaving aside all the problems with what assessors look for, the whole idea of independent evaluation takes us away from where the focus ought to be: i.e. that we know how we are doing, that we can build in methods for improvement and we can work with our suppliers/customers to continually improve performance.
Having the Standard is often, of itself, a barrier to learning and improvement.
The Standard is a red-herring.
Comparability is a red-herring.