I work on a regular base as an instuctor with non-martial artists.
The seminars don't show "normal" self-defense techniques but techniques to de-escalate a physical conflict if possible without hurting the aggressor.
The seminars are meant for staff members who work with mentally disabled persons or persons with psychiatrical disorders or aggressive teenagers ...
The attacks we have to deal with are not very "competent" but very strong and wild. And the people are often heavy.
And In every seminar there is at least one Person who needs to test whether what I teach really works.
I have never hurt anyone.
So if I know that pain causes resistance, why should I use it as a part of technique?
Although I expect you won't like or won't take it serious here is a short clip of Endo about nikyo ...
Very instructive video, and I like Endo sensei's aikido a whole lot, to be honest. I went to a seminar of Dirk Müller in Hamburg a month and a half ago and it was an eye opener. I tried to apply some of the things I learned at that seminar at my regular class. They didn't work at all, mainly because we don't train aikido "with two", as Herr Müller does. In fact, control through pain is very much a part of our curriculum. With that I mean that if uke resists (which we all do) he will feel some degree of pain. The advantage of this is that I have learned (and am still learning) to work with heavily resisting people, or people who aren't naturally supple and subsequentially more prone to pain.
On the video: pulling someone against you when his hand is in nikkyo on your body is essentially controlling him through pain.