After suggesting that we may consider apocalyptic desires (etc.) to be irrational and to provide no reason for acting, Parfit writes (p.119):
[The Deliberative theorist] might insist that his theory is adequate, since those who were thinking clearly and knew the facts would not have such desires.
Whether this is true is hard to predict. And even if it were true, our objection would not be fully met. If certain kinds of desire are intrinsically irrational, any complete theory about rationality ought to claim this. We should not ignore the question of whether there are such desires simply because we hope that, if we are thinking clearly, we shall never have them. If we believe that there can be such desires, we should move from the Deliberative to the Critical version of the Present-aim Theory.
Bizarre. It may be hard to predict whether a desire would be rejected on ideal deliberation, but that is just to say that it is hard to tell whether the desire is truly irrational. For surely persistence on ideal reflection provides the very criterion of what it is for a desire to be rational. (DP then tells us how to derive reasons from rationality. Parfit seems to be doing the opposite: taking reasons as given, and defining 'irrationality' as the objective absence of these.)
Parfit is thus using 'intrinsic rationality' as a term of dogmatic endorsement. He demands that a "complete theory of rationality" be more like the Ten Commandments: an explicit list of which desires are to be deemed 'good' or 'bad', without any need for actual reasoning. But that would be a theory of revelation, not rationality. What we want from our complete theory of rationality is a process of inquiry by which we can discover which desires are ir/rational. We shouldn't expect to be given the answers right at the outset, at least not explicitly. Instead, the theory has implications for what conclusions are or are not rational. This is the only sense in which it "ought to claim" such things.
It's especially strange when Parfit talks about how "[w]e should not ignore the question of whether there are [irrational] desires..." Of course we shouldn't! (Does he really take the Deliberative Theorist to disagree with this?) We should inquire as best we can - undergo a process of rational deliberation, do philosophy - and see where we end up.