Our justifications for working to minimize the pain of our fellow humans aren't neurological. Our justifications for thinking that our fellow humans do experience pain are, in part, neurological (and in part based on our observations of their behavior). Once we have good reason to think that some action of ours does cause our fellow humans pain, then we have a moral reason to avoid that action. That moral reason may or may not be an insurmountable one, but causing a fellow human pain at least requires some appeal to some good that outweighs the pain.

I had assumed that the leap here for most people would be extending moral consideration to non-humans. I'm surprised to see that the leap in this case appears to be extending moral consideration to beings other than oneself.

I am aware of many situations in which suffering is a dramatically positive force

I don't buy this. There may be situations in which suffering motivates some other positive action, but I can't see in what sense suffering itself could be positive -- as in, ceteris paribus, better to have suffering than not to.