as an aiki-jujutsu practitioner I just wanted to add my two pennies worth. Modern Aiki-jujutsu (such as Hakko Ryu & Dentokan) has a humanitarian goal akin to that of Aikido in its philosophy on violence and self-protection. Though atemi is emphasised more, atemi is always employed more as a distraction, such as a mitsubushi rather than as a knock out blow. The Jujutsu technique is paramount, to incapacitate your attacker through immediate pain compliance rather than cause permanent injury. Hakko Ryu's philosophy is no challenge, no resistance, no injury. The art is designed to equip practitioners with the skillset to defend themselves safely and maintain control of their emotions.
Ewen, et al;
Hakkoryu could be considered largely "martial shiatsu", so the atemi is not only always present in each technique, it is a primary component of each technique. For example, there are multiple atemi in Hakko Dori (the first technique in shodan-ge), though they are not strikes in the conventional sense. In fact, the emphasis on atemi, e.g. attacking tsubo, in Hakko Dori -- with Hakko Dori serving as an analogue to Aiki Age (Daito-ryu) and the initiation of Kokyu Dosa (aikido) -- exemplifies what differentiates Hakkoryu from its predecessor and cousin art. Shiatsu can immobilize a person and/or put them to sleep. Knowledge from shiatsu delivered via a strike such as a metsubushi can do the same in jujutsu (i.e. can result in a knock-out).
The founder of Hakkoryu, Ryuho Okuyama, was clear in his writings, e.g.: "[C]almly face imminent peril and move on without hesitation to capture and punish assailants reasonably". "In Hakkoryu, there is indeed no technical skill without a spiritual determination to carry on without hesitation to life or death." So, under certain circumstances, killing could be considered the reasonable response in a given situation of imminent peril. In fact, the shodan-level waza include atemi, that if delivered with full power, would likely cause severe permanent injury or death. However, note how these atemi are presented and continue to evolve as you move up the waza board. Nidan-ge, for example, heavily emphasizes ending threats with the killing blow at the ready but held in reserve.
What Okuyama is saying is to develop self-defense responses to the point they are instinctive -- both in execution and in finding the appropriate level along the use-of-force continuum. Non-human predators kill based on instinct and the need to survive, both to eat and to not have themselves or their offspring be killed by something trying to turn them into a victim/meal. So, malice, the want
to hurt or kill when it isn't needed for self-preservation, may not be part of the equation in Hakkoryu, but the need
to hurt or kill is reasonable and acceptable -- and so it is in common sense and under the law in most modern jurisdictions. As a government-employed correctional officer, Rory Miller's approach to violent encounters must take these things into consideration: it's not just wanton violence as a response to the same.
Regarding aikido, I can't think of a technique off hand that is designed to kill upon contact (though many of the kansetsu- and nage-waza, for example, can readily break parts of the body). That said, I can see how an adept aikidoka could do significant damage with Irimi Nage, for example, as a technique or as the general framework for some other instinctive response to a dangerous attack. The technique/response itself may not involve a strike or a lock designed to inflict damage or death, but the uke could certainly end up quite damaged or dead upon impact with the ground. If the alternative is the aikidoka's own death or incapacitation, would such a scenario be anathema to what aikido's about?