Actions have consequences

Humans didn't always use weapons. We don't have claws or strong jaws so we evolved. We evolved alongside bacteria in our mouths that can trasmite many diseases such as hepatitis B, hepatitis C, herpes simplex virus(HSV), syphilis, tuberculosis, actinomycosis, tetanus, and very rarely HIV. Usually its transmitted from bites but if the saliva enters an already exists wound or in someone mouth these diseasescan be transmitted. We have many diseases in our mouth that are adapted to our body to not harm us but aren't adapted to the environment in others so they can be deadly. These bacteria allowed us to hunt even without weapons and are why we have greater stamina regen than most species and can go days without food while most mammals need to eat daily. We would bite our prey and simply follow them until disease set in and they were weakened or have died. As the disease was caused by bacteria from the hunter it wouldn't cause any issues if the meat was eaten as long as it was only eaten by the person who infected it. It allowed a safer way to hunt and protected our kills from other humans. Also the disease would make it so most predators would avoid eating the carcus. If someones spit enters a wound or you are bitten by a person go immediately to the hospital. Better to be safe then to wait till necrosis starts spreading and they need to cut off a chunk of flesh or amputate a limb.