A couple of recent comments have prompted me to consider my impressions of the cold, dark side of Harry. In particular how it differs from an 'evil, bad side' and why it seems to me to go hand in hand with being 'super rational'.

Someone complained elsewhere (I think it was in the other thread) about Harry being the Boy-who-Lived and having a prophecy and having a cold dark side and being super-rational.

Given that I know Harry to be super-rational and also that he is functional and has a credible ability to achieve goals I would actually be somewhat surprised if he didn't also have a colddarkside. Partly because I am generalising from a sample of me and partly because that cold practicality is required if you are going to maintain rational beliefs about yourself and also function.

Also, from the descriptions it looks like he was fighting this battle in ColdDarkLordHarry mode, so in addition to the above, he might even have been worrying that his Dark Side had subconsciously arranged things (such as a Potions failure, or just the situation of random danger with the Feather Fall potion as a false guarantor of safety) in a way that would bring his Intent To Kill to bear. It might even be revealed later that, for just a moment, his Dark Side produced a desire that she actually die, and that's what's making him feel so guilty.

A caricature of the non hyper-rational person suggests that they have the ability to act in an effective approximately instrumentally rational manner in most typical situations while simultaneously presenting a warm front. The 'dark side' is denied but also harnessed. It 'subconsciously' arranges things to achieve pragmatic ends while maintaining plausible deniability even to yourself.

When you are super-rational you don't have that luxury. The 'cold, dark' instincts must ally themselves with the rational side and the conscious awareness. You don't 'accidentally' kill someone or screw them over with unconscious passive aggression. If you need to kill someone you kill them. If you need to hurt them, you hurt them. The colddark may prompt you to lie but it need not call you to lie to yourself.

The Intent To Kill is somewhat similar. It isn't a a sadistic part of you that secretly wants people dead. It isn't malicious. It is ruthless and practical. If you must fight, it says, then don't fight fair and don't fight half heartedly. If you have a goal then the actions you take should be about achieving the goal rather than adopting the persona of a person who has a goal.