Is it normal to be disgusted by people who remove rats with poison?
I've never subscribed to the philosophy of "well other people are doing it so it must be ok". If you were to visit China and witness the mass slaying of dogs, would you not feel disgusted? There's a very thin line between what's "commonly accepted" and what's not. There’s no golden rule that states that 1 lifeform is worthy of respect while another is not, only arbitrary societal standards.
Usually in the section of the store with the rat poison, next to that there will be other non-lethal solutions that in my experience are just as effective as the lethal solutions.
I don't care if it's socially normal to not respect lower lifeforms, herd mentality is never a good excuse. This goes for all animals, not just rats.