Reprogramming Argument
Humans can't be reprogammed in the arbitrary way that robots can be. The actions of the robot depend entirely on the whims of the programmer, whereas human behaviour is self-determined.
For instance, a robot can be programmed to act tired no matter what its physical state is, whereas a human normally becomes tired after exertion.
Paul Ziff, 1959.
The Ziff argument
"If we think of robots being put together, we can think of them being taken apart. So in our laboratory we have taken robots apart, we have changed and exchanged their parts, we have changed and exchanged their programmes, we have started and stopped them, sometimes in one state, sometimes in another, we have taken away their memories, we have made them seem to remember things that were yet to come, and so on... And what we find in our laboratory is this: no robot could sensibly be said to feel anything. Why not?" (P. Ziff, 1959, p. 67).
"Because robots are replaceable. Because robots have no individuality. Because one can duplicate all the parts and have two virtually identical machines. Because one can exchange all the parts and still have the same machines. Because one can exchange the programmes of two machines having the same structure" (P. Ziff, 1959, p. 68).
References
Ziff, Paul. 1959. The feelings of robots. Analysis 19(3), January 1959: 64-68.