Neuroscientist here, This line of reasoning is not contentious at all. We are the only species that in a short amount of time (evolution terms) changed so drastically and it is generally agreed upon that it is because we learned to hunt and cook meat, extracting way more calories from that. That also cleared out schedule enough to be more social and inventive.

No other animal cooks meat.

After thousands of years of evolution eating meat and relying on it for many vitamins and minerals it is not so simple to remove it entirely without consequences. Plant protein, and some vitamins and minerals do net get absorbed efficiently. Studies have shown the possibilities of health issues. That sound like a moral argument to me. harm to animals Vs. harm to self.