The AI Castor cant live outside the matrix, therefore for the survival of the real castor to come about the one who cannot survive outside the matrix must be the one to drink the wine. Although we are the same person here, we all know that this world is base don deceptions. If the castors are the same they will both want to get out so that Castor can continue to fight the good fight for zion. Castor cant do that if the real one drinks the wine and dies. That means the AI has to drink the wine in order the real castor to live and do what both the AI and Human Castor want.
The AI can not operate alone. Where would he get his weapons, who would be his support. To do what us rebels do it takes more than one person. Suppose he is in a tight spot and cant get away, he cant jack out, then hes fudged. Thats the end of castor, and you cant help the resistance when your dead. Its about the survival of the person best suited to help zion. That is the human castor. He has more resources and is able to get orders directly from Zion. The clone wouldnt be able to do those things.