Alexander Pruss argues for the following: "given soft determinism, it is in principle possible to avoid culpability while still getting the exact same results whenever you don’t know prior to deliberation how you will choose. This seems absurd, and the absurdity gives us a reason to reject the compatibility of determinism and responsibility."
Pruss asks us to suppose, for reductio, that determinism is true and that we are morally responsible for our actions. Then he tells the following tale:
...imagine a device that can be activated at a time when an agent is about to make a decision. The device reads the agent’s mind, figures out which action the agent is determined to choose, and then modifies the agent’s mind so the agent doesn’t make any decision but is instead compelled to perform the very action that they would otherwise have chosen. Call the device the Forcer.
Suppose you are about to make a difficult choice between posting a slanderous anonymous accusation about an enemy of yours that will go viral and ruin his life and not posting it. It is known that once the message is posted, there will be no way to undo the bad effects. Neither you nor I know how you will choose. I now activate the Forcer on you, and it makes you post the slander. Your enemy’s life is ruined. But you are not responsible for ruining it, because you didn’t choose to ruin it. You didn’t choose anything. The Forcer made you do it. Granted, you would have done it anyway. So it seems you have just had a rather marvelous piece of luck: you avoided culpability for a grave wrong and your enemy’s life is irreparably ruined.
(1) If the Forcer is activated on an agent, then (i) the agent does not make a decision to perform the action and (ii) the action is compelled.
(2) If the Forcer is not activated, then the agent (i) makes a decision to perform the action and (ii) the action is uncompelled (i.e. the action is performed willingly).
(3) Therefore, it is possible for an agent to perform an action for which she is not morally responsible even though had she been given the chance to decide she would have performed it any way.
(4) (3) is absurd. Therefore, compatibilism is false.
Here is a problem: the argument does not entail the falsity of compatibalism. The compatibilist is committed to the view that what makes a person responsible for her actions is that the action is performed willingly (uncompelled). If a person is compelled against her will to perform an action, then she is not morally responsible. So, it is true that if that is the case, then the agent is not morally responsible. But it does not follow that determinism is false. What follows is that it is possible for agents to perform actions for which they are not morally responsible. (1) - (3) do not entail (4). Leaving off from (4), this is what follows:
(4)* If an agent does not make a decision to perform the action and the action is compelled, then the agent is not morally responsible for the action.
(5)* The Forcer is activated.
(6)* Therefore, the agent is not morally responsible for the action.
But that is perfectly compatible with determinism.
Furthermore, it makes no difference whether the action would have been committed willingly if the agent had been able to decide for herself. People cannot be responsible for actions they would have committed if they had been given the chance to decide. I'm sure there are all sorts of things we would choose to do if we had thought about them. But we are not morally responsible for any of those things. So, why would any agent who doesn't decide to do something and is compelled to do it be held morally responsible?
It is also not clear that it is possible to make no decision and at the same time be compelled to perform some action. Surely being compelled to do something is to be forced to do it against the will of the agent. If so, then the agent has already decided not to do the action.