Many manufacturers believe that selling their product or device without FDA approval is acceptable. 

If people buy it, but is this breach in ethics worth the potential consequences?

If caught marketing an unapproved product, the FDA may issue a warning letter requiring the correction of such violations, in hopes that the manufacturer will take initiative to abide by the law. Depending on the circumstances, if voluntary compliance is not reached, this warning letter can come with or be followed by legal enforcement strategies such as recalls, seizures, administrative detention or prosecution. However, not all cases require a warning letter to be issued before legal action takes place and in many instances this has ended in significant fines and jail time.

Most importantly, having an outside party approve your device or product is necessary to ensure the safety of all patients. Death or injury of a patient can occur if the proper approval process is not utilized. Although the costs associated with such approval processes may be intimidating, selling your product without FDA authorization is in no way worth the risk.

Source: FDA site