I'm with Deb in the sense that the key thing is giving the uke a sense of being 'urgently compelled to move.' I disagree with her, however, if she is saying that it is the implied and consciously understood threat of pain the induces this urgent compulsion.
I have a very high pain threshold and pain is rarely something that compels me to move. Certainly it is not fear of pain that drives my uke. I was taught that uke goes best if you take him where he was going anyway. I was taught that pain -- caused or threatened -- causes uke to stiffen and interferes with their ability to respond appropriately to technique. I was taught these things not through discussion and theory, but through a practical understanding as uke and nage of what does and does not cause people to move. My experience says that pain causes immobility, stiffness, tension, and conflict, and is not a good basis on which to build your technique.
At this level, it's not about the morals. It's about what actually works.