Article IV of the constitution, which includes the full faith and credit clause ensures that "laws passed in one state are honored by other states."
This is done to prevent states having fights with each other and to keep a common war or anything comparative. This applies to laws one of a kind to the state since government laws are the same for all states. This for instance is the privilege to have a capital punishment. Different states need to respect the way that there's such a law and can't trouble the state about it since it's not something found in a government law.