Why do you think an "enemy" or scapegoat is necessary for the animals? Why does the "enemy" have to change? If there were no "enemy," what would that mean for any society, including that of Animal Farm?

The scapegoat is to serve as a deterrent for others, to let them know there are consequences for each action. The enemy changed from the farm owner to the animals themselves. If there were no enemies there would be no need of a scapegoat, we can finally have a society that one doesn't need to watch his back always