To add to this, that behaviour would typically be OK in the US, with a good compliance department to keep you away from the worst of the grey areas.

If the SEC did investigate you for this, an important part of the case would turn on the extent to which your actions were "bona fide market making". And the regulator would also be more introspective about the market structure that allowed this to happen - why is there only one market maker? How did we allow a derivatives market much more liquid than the underlying?