Rights are granted by the government, not by nature or any kind of God. People gain rights by fighting for them and gaining concession from leaders. Many cultures have had slavery. Rights are only gained by political struggles over many years. No one will grant rights to people unless they earn them.
Even if fundamental rights are technically in the realm of opinion, they should be treated as reality. Society performs better and people are happier knowing they have rights considered fundamental and not subject to violation. The rights of citizens is the core of virtually every significant government in the world. While not all governments honor the rights they claim to give to their citizens, people are proud and protected when their rights are upheld.