Consider cases where an agent is brainwashed into having to choose A by having a set of desires implanted that are sufficiently strong to motivate her to choose A. Here's a rather rough argument:
- In these brainwashing cases, there is no ability to do otherwise.
- The relevant difference between these brainwashing cases and cases of agents in deterministic worlds is the history by which the agent came to have those desires.
- The ability to do otherwise is independent of history.
- So the relevant difference between brainwashing cases and cases of agents in deterministic worlds does not make a difference for the ability to do otherwise.
- So agents in deterministic worlds are unable to do otherwise.
Basically, the point is that while compatibilists can perhaps get out of manipulation arguments by insisting that history makes a difference between cases of brainwashing and cases of determinism, since history makes no difference for the ability to do otherwise, manipulation arguments succeed for the ability to do otherwise, even if they fail for freedom.
There have been two kinds of compatibilists. The Humean compatibilist, well represented by Lewis, have held that determinism is compatible with the ability to do otherwise. The Frankfurtian compatibilist instead insisted that freedom does not require the ability to do otherwise. If my simple argument succeeds, compatibilists must be of the Frankfurtian sort.