I would like to point out that the one strike/one kill was valid back when the Kata were created, and practiced in the early days. The Karateka of the time constantly trained and conditioned the body parts, and their skill to accomplish that skill. Not so much anymore, while the same kata are practiced. So, maybe it is a good question about changes needed to make them more effective for today's practioners.
As I've mentioned before. ikken hisatsu "one strike one kill" is not traditional in Okinawan karate. Japanese karate borrows it from kendo.
OK. The idea in kendo was that the ideal the swordsman was aiming at was a literal kill with the first strike of the blade. Given what a katana can do if properly handled, the idea of `kill' in `one strike, one kill' is literal. But it doesn't have to be interpreted that way. In
The Way of Kata, Kane & Wilder paraphrase the idea as their second principle of kata application as `Every technique should be able to end the fight immediately'. Given a set of interpretations for a kata move, pick the one which has the greatest odds of putting the attacker out of action. In last month's
Black Belt , there's a long article on the `modern' sense of one strike/one kill which pretty much comes to the same conclusions. Given what is described as a `block-block-punch' sequence, look for the interpretation of the moves which has the most damaging effect on the attacker.
Now, if you say that you don't accept one strike/one kill on
that interpretation of the saying, what would you suggest to make the kata applications `more effective for today's practitioners'? The ethic of 1S/1K already seems to be, find the most destructive application you can. If you give up 1S/1K, it seems as though you'd be taking the position that you shouldn't seek the kata interpretation which caused, or allowed you to set up as soon as possible, the most damaging interpretation. Wouldn't this then be a
retreat from maximum effectiveness?
I can imagine that two people could disagree over what the most damaging application was. But if 1S/1K means, use the technique which is most likely to disable the attacker most severely, then the two people who are arguing are both accepting 1S/1K; they just have different ideas about which way of implementing is the best in practical terms. That's not the same as rejecting it in favor of a different strategic approach to the fight.
The question of body conditioning is relevent here, because a kareteka who's done a lot of that sort of thing may be in a position to make a given move (not necessarily a strike) `lethal' in the 1S/1K sense, whereas practitioners who haven't might not. For the latter, a different move might be more effective. But again, the question wouldn't be 1S/1K itself, but how best to implement it given the capabilities of the fighter in question. For both the conditioned and unconditioned fighter, 1S/1K means that those two `blocks' in sequence had better not correspond to a sequence of defensive deflections in a fight---there is presumably a better, more destructive interpretation of the motions described as `block-block', and your job in working out the bunkai is to find it (or several, and decide which is the most damaging one in terms of your own physical capabilities and fighting strengths)...