Full Idea
The main problem faced by non-cognitivism is known as the Frege-Geach problem: if I say "If murder is wrong, then getting your brother to murder people is wrong", that is an unasserted context, and I don't necessarily express disapproval of murder.
Gist of Idea
The Frege-Geach problem is that I can discuss the wrongness of murder without disapproval
Source
Alexander Miller (Philosophy of Language [1998], 9.2)
Book Reference
Miller,Alexander: 'Philosophy of Language' [UCL Press 1998], p.281
A Reaction
The emotivist or non-cognitivist might mount a defence by saying there is some second-order or deep-buried emotion involved. Could a robot without feelings even understand what humans meant when they said "It is morally wrong"?
Related Idea
Idea 6969 Approval of historical or fictional murders gives us leave to imitate them [Ayer]