You really think that captures what these guys were doing with their lives? Obsessive-compulsive, consuming drive towards training for "martial strength" and power?
Is that why Ueshiba went to Mongolia to help found a utopia? Because he thought it was a path to internal power?
I think in Ueshiba's case, "martial power" was a trivial, childish goal as he got older. His training was aimed at becoming a conduit of the kami, and to that end his aim was to be able to attain a state of open awareness and a totally uncritical non-consciousness.
As to why some Aikido teachers have reputations as brutes, two words: Imperial Army.
Having had little exposure to "mainstream aikido," I'm not really familiar with any of the "brutes" among the most well-known teachers, but I believe very few of those were in the Imperial army. They were post-war students of O Sensei who just got mad with power, especially after they found what aikido technique, alone, could do against much larger westerners. They began to feel like gods, especially with all these westerners bowing and scraping to them and treating them like gods.
However, these were the same people who didn't understand O Sensei's words and mostly rejected all his spiritual teachings, which in large degree turn out to be allegorical instruction on using yin and yang in the body. And while O Sensei was thrusting a spear into trees, alone, and doing all his solo martial training, these students were doing the typical Japanese social thing of getting drunk and steeling themselves for the next day's efforts--using will power and muscle to bear the heavy load of all that training. It did make them godlike to naive westerners, but it left them with tremendous gaps in their knowledge, including deeper understanding of what it was in their training that had made them so strong--even though they never approached the mysterious skills of O Sensei.
So mere "mainstream aikido" training made them physically very good, but also produced a lot of people who were womanizers and bullies--not that I've ever encountered such people, but I can say that the "tough" schools I've encountered tend to be safer than the "spiritually" oriented schools because everyone knows why they're in the tough school. At the "spiritual" places, it's a weird mishmash of half-martial/half-spiritual, the "martial" side being overly casual and vague, and the "spiritual" side is a mishmash of the teacher's idiosyncratic interpretation of some mistranslated words from O Sensei....while the whole thing parades under an imitation of the martial strictness of the more famous teachers.
And none of these people begin to approach O Sensei's abilities.
Mark has done a great job of profiling four major aiki masters: Takeda, Sagawa, Horikawa and Ueshiba. All, clearly, had devastating physical power, but none were famous for hurting people in general. We mostly know about aiki and the masters mentioned because of Morihei Ueshiba's spreading a version of the art as aikido. So we have 10,000,000 practitioners of aikido (according to Lee, at least), but almost none of them have power like the masters mentioned above. However, in aikido, we do have a lot of dirty-shot artists and in my experience, these are found mostly among the "spiritual" adherents, who get easily frightened by a little realistic technique and respond with violence.
We often make the mistake of thinking that Morihei Ueshiba was really more spiritual than the others mentioned, but we don't really know much at all about the spiritual beliefs of the other people (except, as Chris Li noted, the document posted in Sagawa's dojo that sounds exactly like the things Ueshiba said). Ueshiba did not become more famous than all the others because he was fantastically more skilled than they, nor because he was a "better" human being (though, apparently, he was truly a great person), but because he was a proselytizer who wanted to develop a huge following around the world. Sagawa and Horikawa seem to have been just as skilled as Ueshiba, but they preferred to retain the ancient truths intact, while Ueshiba was happy to send out thousands (or tens of millions) to do a standardized physical routine which only hinted at the deeper content, and that form was then distorted by the intellectual errors of those who felt themselves able to understand words that had already been mistranslated.
No question about it. You have to look far below the surface of modern aikido to understand its place in history and its true import on the spiritual level.