In the Cartesian tradition that replaced it (which still informs most popular 'thinking' even now I reckon), the soul 'inhabits' the body like a ghost inhabiting a machine. From this it seems to follow that a person has to be able to exercise his rationality before being considered alive; otherwise, the 'ghost no longer inhabits the machine', and you can do whatever you please to the empty shell.
And in the third place, there is materialist-nominalism, which informs most elite 'thinking' today (showing that the elites are dumber than the general population, since materialism is dumber than Cartesianism). This thinking says there is no such thing as a person and you can do whatever you like to the piece of meat lying in front of you, provided it won't get you into trouble or make you feel bad.
And by abandoning Thomism in the mid-twentieth century, Catholics have thrown down the intellectual weapons with which to fight these evils, and allowed this kind of situation to come about. And nobody takes us seriously because we're forced to fall back on a revelation that (logically) can only bind believers' behaviour. What a disaster! Kyrie eleison!
I suggest you recommend Feser's Aquinas to your readers. It gives a tremendous overview of this kind of thing.
And I do recommend this book. Also, Edward has a blog at http://www.lightofhumanreason.com/
