Some people value Christian ethics, but deny that Christianity itself is true. This makes no sense. The truth of Christian ethics is directly dependent on the truth of Christian metaphysics. If Christian metaphysics are mistaken, then the ethics that flow from those metaphysics have no basis in reality (on the Christian worldview).
Granted, it could still be the case that Christian ethics are still true in toto or in part, even if Christian metaphysics is false. But in that case, they are true in virtue of the truth of some other metaphysical worldview or meta-ethical system. So why continue to embrace these ethics as CHRISTIAN ethics if their truth is grounded in something other than Christianity? It’s one thing to affirm that Christian ethics are true even if Christianity isn’t, but it’s another thing to subscribe to Christian ethics as CHRISTIAN ethics while denying that Christianity is true.