I suppose at some point we'd need to have a discussion on what we mean by words like "attack" and "balance."
To expand on what Hugh said, I think of "attack" as morally neutral. An attack may or may not be aiki. It may or may not be balanced. My body's immune system attacks pathogens. When in balance, it kills and destroys in a proper proportion. When not in balance, its response is too little and I become ill. When exaggerated, I have an allergic reaction.
Predators attack prey. Success in survival is often a matter of being able to attack while closely adhering to a zone of balance. On the mat, we spend around half our time learning how to be the attacker, and none of this should be time spent outside of aiki. I might go so far as to say that without uke, there is no aikido.
Uke may sometimes simulate the bad guy, in order to help tori learn. But some encounters (on or off the mat) require us to be primarily uke, and in this mode I believe we still should try our utmost to exemplify aiki and the qualities of balance.
Just a thought.
I would reverse what you say there myself. From the view of spiritual, mental and physical.
When you say morally neutral I would say that equals no need to attack anything.
So I would say when unbalanced is when something or someone attacks.
Philosophically I would say predators had to learn to kill due to lack of available dead food. (for they are meat eaters)
Does a body attack pathogens? Yes, when it's unbalanced. When in good balance it's healthy and merely utilizes what comes in and disposes of the rest. But there again are we not trying to be better, more enlghtened, improved?
Most like to think it's natural or normal to kill and often point to 'nature' as a justification. Thus no matter how technically advanced they get they are still unadvanced themselves, unbalanced.
Thus kuzushi, taking balance. Physical. Lead the mind and that's mental. But get good enough and I say you can return balance to the unbalanced attacker and so it would be more of giving back kazushi or balance.
It can be done and Aikido can do this.
Anyway, such is my way.