Final answer:
The inmate is justified in insisting on exercising his religious rights based on the Supreme Court case Estelle v. Gamble.
Step-by-step explanation:
The inmate is justified in insisting on exercising his religious rights based on the Supreme Court case Estelle v. Gamble. In this case, the Supreme Court established that inmates have the right to practice their religion, and prison policies must reasonably accommodate those practices unless there is a compelling governmental interest. Therefore, if the Sikh inmate's refusal to shave his beard is based on religious grounds, he can assert his religious rights protected under the First Amendment and the Religious Land Use and Institutionalized Persons Act (RLUIPA).
Learn more about Religious rights in correctional facilities