Disagree. According the the HIPAA/HITEZCH Omnibus rules, the patient has the right to restrict their protected health information (PHI) from being released to their own insurance company.
The patient can request that you not file insurance, and pay cash, if they request it in righting. They must pay in full, at the time of service, and they can pay the regular rate.
Incidentally, they can also pay a slight discount as a 'prompt pay'. This prompt pay discount is permissible, as long as you allow any patient, without discrimination, the same opportunity for a prompt pay discount.
Here is some information on HIPAA Omnibus rule...
https://www.aapc.com/blog/22440-know-when-hitech-trumps-payer-contracts/