It makes sense! I finally understand it!
This is the first Christian I have ever heard to even make a lick of sense when talking divine command theory. Is this what most people mean when they invoke command theory and purpose arguments? Why the hell could none of them ever make the argument as clear as this fine (but wrong) Christian fellow did in the first Christian speech of the debate?
That's what they mean. They understand morality to be "what are humans supposed to do?". I can agree to that phrasing. Then they jump to - they claim - an equivalent formation: "what is the purpose of humans?'. I never saw that particular linguistic leap before so clearly. It really is that simple. They understand "ought" statements only in terms of purpose. It makes so much sense now.
I totally understand how one can go from "What is the purpose of X?" to "What is X supposed to do?". Makes perfect sense.
Of course, the problem is equivocation. The equivocation is laid bare with the question "Why should we behave according to our purpose?". More lengthy, you can bring out the usual dilemmas, such as "If our purpose was to rape women for fun, should we do it? Should we fulfill our purpose?". The moral answer is no.
But, I feel like I'm so much closer now to understanding divine command theory. They confuse "what should we do?" with "what are we supposed to do?" and then to "when you ask what is something supposed to do, you're asking what is its purpose". The flaws are so obvious when you say it like that, but the fallacious reasoning of the Christian is so much clearer.
I feel wonderful.