Miller proposes an argument against emotivism which I think does not work.
According to emotivism, when I sincerely utter the sentence “Murder is wrong,” I am not expressing a belief or making an assertion, but rather expressing some non-cognitive sentiment or feeling, incapable of being true or false. …
But what about… “If murder is wrong, then getting little brother to murder people is wrong”? … now there is a problem in accounting for the following valid inference:
(8) Murder is wrong.
(9) If murder is wrong, then getting your little brother to murder people is wrong.
(10) Getting your little brother to murder people is wrong.
Consider the following example:
(a) If abracadabra, then hocus-pocus.
This looks like a valid modus ponens, but if abracadabra and hocus-pocus cannot have truth values, it is nothing of the sort. It’s entirely meaningless.
Similarly, if (8), the minor, has no truth value, then (9), the major, has no meaning; the apparent inference collapses; and hence (10) stays undefended; moreover, (10) itself seems to be a moral statement and as such, like (8), lacks a truth value.
Which is perfectly fine as far as the emotivist is concerned.
If the concern is that (9) seems true, then in denying not only that (8) is true but that (8) has a truth value at all, the emotivist has already proven himself perverse beyond hope. He would have little compunction denying in addition that (9) is meaningful.