> A free will is a healthy will, in the sense that our decision mechanism is not broken by e.g. drugs, electrodes or mental illness.

Isn't the drug example a contradiction? If my brain was healthy ("free") when I decided to take drugs, why would the resulting drugged state be less "free"? After all, it was my "free" choice to take the drugs and alter my mental state.

Edit: Also the definition of "mental illness" is somewhat nebulous and not historically fixed. Homosexuality was at one point called a mental illness.