Re: Locking/pinning as pain submission...
I too at one time assume locks as pain submission and the desired outcome is that the uke will tap out due to pain. But then after reading some of the post around the forum, I realised that pain alone is not enough as per discussion in the aikido vs. drunk and druggies thread.
By going back to basics... aikido osae is literally immobilization. This means locking out the joint physiologically such as hyper extension where the uke cannot move the limbs physically and not due to pain alone.
Hence I would agree with you that pain alone is a poor motivator to deter any aggresive intend (if this is what the gist of your post is all about).
To illustrate... just recently in class as we are doing gyaku yokomenuchi (reverse side strike) kuzushi nage. I have done this technique countless times and it was not something new. In my mind, the essential ingredient of the technique is kuzushi (breaking of balance) and some wrist manipulation. It usually work.
However, the adjutant sensei was being nasty that night and he said, "Stop Stop, Not like this". Then he point to the logo of our dojo and said do you understand? What is there to understand, I thought. It is only a plain image of an eagle pearching on a branch. Then he showed me his variation of kuzushi. It was a whole new experience.
His technique included...
1) breaking of balance <checked>
2) wrist twisting <checked>
3) Vice like grip...
Due to the added element of very strong grip, my whole limb was in his control, I could not twist nor turn at all if he did not allow me to. Then I realised what he meant by the image of the eagle. One must have very strong grip like those of an eagle's claws.
This bring me back the thread, immobilization is the key not pain. So much to learn, so little time. Sigh.