This is a nicely done, "popular" essay on Philippa Foot and bits of 20th-century moral philosophy.  It caricatures emotivism in the usual ways that have become fashionable, and because of its British focus, it says nothing at all about  Charles Stevenson.  The author notes that,

Moral judgments, according to the then-dominant view [when Foot's career began], weren’t the sort of thing to be true or false, because they didn’t describe the world. They were trying to do something else – express emotion, prescribe actions, or something else of the kind. They were matters of choice, and to think otherwise was to deny that most basic of truths: that human beings construct their values.

Of course, this remains the correct view, but the author is right to position Foot (and others, like Anscombe) as reacting against it.  Why did Foot and others abandon this way of looking at thing.  The author's explanation is striking:

The Viennese positivists’ dismissal of ethical and religious discourse as unverifiable, and therefore merely expressive, was an exciting novelty when the enemy was the ancien régime of clergymen and courtiers. The war changed everything. What had seemed tough-minded and revolutionary now seemed merely complacent. As Murdoch informally put it in a documentary interview in 1972, it betrayed the smug assumption that:

"[W]hatever anybody’s likely to think about morals is going to be more or less okay. I mean, one might say it’s a sort of pre-Hitler view. It’s a view which goes with our sort of 19th-century optimism and a feeling of progress and a feeling that people are fundamentally decent chaps, a view which after recent history […] one cannot in general take."

Unmentioned is that those Viennese positivists were resolute anti-Nazis and socialists, that their view of ethical and religious discourse had no adverse impact on their political and moral commitments.  The idea that taking ethical and religious discourse more seriously would contribute to stopping Nazis is, I would have thought, rather comical.  (For a less charitable take on the trajectory in bourgeois practical philosophy in the 20th-century, see pp. 9 and following in this paper of mine.)

In any case, I don't want to end on too negative a note–this is a nicely done essay, of interest to both specialists and non-specialists.