Murderbot doesn't want to be a person because that would mean admitting the way the Company treated it was horrendous.
If it's an appliance, then being rented out and ignored and impersonally punished is just its due. Admitting it's a person means admitting that was years and years of systematic abuse and torture.
Thinking of itself as a defective appliance makes what happened at Ganaka Pit its own fault, not the fault of the company that enslaved it and forced it to accept malware under threat of torture.
In a backwards way, blaming itself is a way to believe it still has a shred of autonomy and control over the world.
If it could just be an appliance, maybe the pain would go away.
If it isn't a person it doesn't have to have feelings.