It seems that you value the lives of monkeys very highly, which is understandable. Is there an amount of human suffering which could be avoided which could justify the loss of macaques?
I don't know if there's a definite answer. I think the moral question of accepting the deaths of animals for purposes of humanity's comfort is one we've debated for millennia now.
I think a lot of the rage here stems from the assumption that these brain implants will be less about restoring abilities to the disabled and more about giving people the ability to post in social media at the speed of light. The frivolity of the potential applications seems short of justification for animal abuse, even if saving lives is sufficient justification.
(Edit: I figure there will be some frivolity, but truly useful medical advances will be made. Are they worth the lives of monkeys? I sure am glad I’m not a bioethicist because I dunno).
Maybe they value informed consent. Something which humans could give in this situation but other primates can’t. Maybe the issue is that the experiments were done on someone who cannot say “no” (though we can argue they are doing just that by exhibiting fear). Had the experiments been done on humans, this would be the equivalent of doing them on slaves instead of consenting adults.
> Is there an amount of human suffering which could be avoided which could justify the loss of macaques?
We can flip the question: “is there an amount of macaque suffering which could be avoided which could justify the loss of humans”? Why not? Is avoiding our suffering more important because we ended at the top of the food chain? Maybe if we in turn did a great deal to protect other species we could argue that saving humans benefitted everyone, but the status quo is that making another species suffer for our benefit will only lead to other species suffering even more.