If rights don’t matter, or if rights don’t exist, then nothing you do to others can be wrong. Wrong means it violates someone’s rights.
Some say it’s not about rights, it’s about power. The power to do things to others. They usually say this to justify government actions that clearly violate individual rights (such as governing).
But if this is true, it's true for freelance criminals as well.
If you justify government this way, why claim a rapist is doing anything wrong? How could anyone make that claim? If there are no rights to be violated, by what basis can anyone say he shouldn't do what he's doing? He has power and is using it— and I hope his intended victim has the power to stop him. Permanently.
Saying rights don't exist, or don't matter because they are just a mental construct, is dumb and is setting yourself up for a really bad end.
People who don’t “believe in” rights had better watch their backtrails. Those who believe them might act on the belief.