Not gonna argue with him, either, but I couldn't resist snarking along the general lines of, "You can't eat it, heat with it or ride it to market, so what's the point?" This is a tiny corner of the general scientific argument against teleological explanations of natural phenomena, "because whether they are true or false is argued to be beyond the ability of human perception and understanding to judge."
If you look at that long enough, though, it will dawn in a delightfully Gödelian spiral that it is also beyond human perception and understanding to know the truth or falsity of that statement. (And so on).
So, as I asked, why bother to defend (or, for that matter, attack) teleology?
His reply was not a stern lecture on philosophy or the weight of history, not an argument from utility (and I've observed him do that quite brilliantly). Nope, simply this:
Hey, it's the Internet! Why not?
It doesn't sidestep or confront unknowableness; it subverts it. There may, in fact, be a higher purpose; maybe he was put here present the argument, to have the discussion...or it may be an end in and of itself.... Or maybe it just happened.
I dunno. How could I?
This reminds me -- the Hofstadter's Law T-shirts are still running way behind schedule. Really thought we'd planned for that.