Ugh. Without paragraph breaks, the above is very unpleasant to read. Please add more structure to your posts.

some humans cannot experience pain

Human vegetables cannot experience pain. Some aware humans may not experience pain from being burnt or cut, but they still experience emotional and psychological pain. This is a very important distinction. I think much of the suffering we cause animals is in the latter categories, although I think they have far less ability to experience such (so the same situations cause far less pain then they would a human).

That said, if we treat and kill animals humanely, their deaths don't bother me unless the animals seem aware and intelligent enough to be invested in goals that we might be thwarting by ending their lives.

Likewise, if we could engineer animals so that they could not feel any sort of pain or distress, physical or emotional, I don't think I could object to any sort of ill-treatment. I wouldn't necessarily approve, but that's more of a squick thing than an actual offense to my morals.