Agree that exclusivity-offerers tend to be exclusivity-demanders as well. But does this stay true given that they also say "Okay, you be poly"? That would seem to screen off a lot.

(Edit) To expand: demanding exclusivity from one's partner has perks (chiefly, exclusivity). Not demanding it also has perks (Eliezer gives examples). Given that someone wants one partner, they're likely to prefer the first set of perks to the second. Given that someone wants one partner and does not demand exclusivity from them? Seems much less clear to me.