DFC
Other than nebulous arguments like "public confidence" (let's face it, Joe Public cannot spell "Certificate of Airworthiness" let alone tell you what it is) or "why bother having the CAA", can you offer some examples of HARM that resident N-reg does?
In GA, the number of N-reg planes is always going to be very small - because commercial/training work has to be G-reg, and for non-IR private owners the Private CofA has a comparable maintenance regime. Anyway, practically nobody goes N-reg to save money on maintenance.
So why bring in restrictions?
Make a case, objectively.