weaknesses of natural moral law
religious : it is based on a belief in God, if we reject God can the theory still stand, or is it deemed useless
telos : focus on purpose creates an issue for humans, the view that everything has a telos imposes an idea of order and design on the universe, and how are we meant to know what our purpose is? eg. NML says the purpose of sex is reproduction, so it doesn't make sense for sex that is not reproductive to be pleasurable
too focused on reason : human reason should not be a basis for morality, it is flawed. Barth argued that NML relied too much on reason when humans have been corrupted by the fall