Patient wants me to lie to insurance. What do I even say?

Patient came in for a crown. Their insurance doesn't cover it because it's "cosmetic" (it's not, but that's what the insurance says). Patient asked me to "code it differently" so insurance will pay. I explained I can't do that, it's fraud. Now they're upset and threatening to go elsewhere. I know another practice in town that would probably do it. Am I being too rigid? Or is this just the cost of doing things right?