The modern form of the philosophical (or meta-ethical) problem of moral realism may be thought to confront a greater test than its predecessors. Its peculiar challenge was famously expressed in Dostoevsky’s The Brothers Karamazov: ‘If God is dead, then everything is permitted.’
Among the more influential philosophical doctrines of the twentieth century was logical positivism which claimed that moral statements are essentially meaningless since they are factually uncheckable. Ethical judgements were defined by the leading English proponent of logical positivism, Freddie Ayer (1910-1989), as emotional ejaculations entirely devoid of reason.
https://drb.ie/articles/climbing-mount-improbable/