Full mouth vs single tooth dentistry

What do you do in cases where a patient wants/needs crowns in Mx anterior 6-11 or 7-10 but has lost posterior teeth and won’t replace them. It will cause the crowns to eventually fail without posterior support.

What if the patient is losing mandibular teeth but wants 7-10 crowned first and may not follow up with mandibular crowns/partials/implants.

Is it ethical to still do the Mx anterior crowns if you know they will eventually fail without full mouth rehab.