After all, when the pilot goes to the potty, who is flying the airplane? The computer? LOL. When something unanticipated goes wrong, the computers are COMPLETELY USELESS because it wasn't programmed to deal with unanticipated problems.
Me, I'll pay a bit extra for my flight to have 2 pilots.
Pilots:
1. fall asleep
2. get distracted
3. make mistakes
4. misinterpret what is going on
5. panic
6. have heart attacks
7. take breaks
8. use the wrong checklist
9. have bad days
10. forget to watch the airspeed and altitude
11. skip steps on the checklist
I.e. are human.
And so a backup is needed.