The same way gravity exists with or without government. There could be a law against gravity but it would still be the natural order and natural law.
The concept of Natural rights is that they exist in the natural order. It is a statist concept to say that government can only give you rights. Government does nto exist to grant you rights, it exists to punish those who defy the natural order and violate the rights of others. It cannot grant extra rights that you didn't already have.
Simply put government exists to punish/protect through deterrance of punishment those who would violate our natural rights. The constitution exists to protect us from the government going over reaching past this limit.
Any law that goes against the natural law is immoral.
Have you people read john locke? Good god...