Imagine that you have a sore throat. The doctor says it is a bacterial infection. Why would you conclude that it is not caused by Archaebacteria?

Archaebacteria are typically not found in the human body, so it would most likely not be the bacteria that causing the infrection.

Most archaebacterial are extremophiles, meaning they love extreme environments. Archaebacteria live in high heat, very low heat, methane, high salt, high pressure, and other places where most other living things can't survive.

If an archaebacteria did manage to get into your body, it would not have the conditions it would need to survive. It would die before it did any serious damage to your body.