Of course, the euthanasia option (where the individual in question makes a concious choice to administer the treatment themselves) should really only be open to those that have been judged to be of "sound mind", and so are making an objective choice, not one thier inner demons are making for them. Of course, I have no idea how you could implement such a system in a fair and even handed manner.
There's also the case where innocents would take this option as well. Suicide in the face of false accusations happens more often than is comforting. Even if you're innocent, the stigma of being accused lingers long and painfully. There's also the fact that rehabilitated criminals are basically screwed when it comes to a potential future. It's not unknown (though I certainly don't know the numbers for it) for a released criminal to get themselves jailed again simply because they can't manage to survive outside the prison system. Society is incredibly hostile to "ex-cons."
That'd be an issue that would have to be addressed alongside the rehabilitation, but it's arguably an even larger and more difficult one to address
Those that can be considered to be of sound mind aren't those that would be eligible for euthanasia.
Not necessarily: Re: Aquizzar's passion murder. I've actually known someone in a similar situation (life imprisonment for murder under the influence), who was entirely of sound mind when sober. There's equivalent situations. Sometimes, especially (but not limited to) when substance abuse is involved, it's incredible dangerous to 'fix' the problem and let the person free -- it only takes one slip up, one mistake, and people are dead or worse as a results.
*This is ignoring the question of, if we really could "rewire" these people to be productive members of society, should we? Would it be ethical to? Something a science fiction writer should explore (and probably has, somewhere).
It's been explored -- not just in science fiction -- yeah, and comes up fairly often. Hell, it was a fluff point in Starcraft -- most of the marine troops on the Terran side are criminals turned into cannon fodder. This, however, is a slippery slop from hell a thousandfold worse than the death penalty.
The simple question is simple: If you can do this to criminals, why not everyone? What's stopping you once you've "rewired" a sufficient portion of the population to simply go on and do the rest? This sort of technology is
absolutely terrifying, for all that it could have tremendous beneficial effects. In one fell swoop, you could eliminate all the little niggling side factors of your society and transform the whole thing into 40 hour work-week nuclear heterosexual <insert religion> families, quietly sending every other child into your military (assuming you haven't gotten your hands on the brains of all the other societies, and now control the world).
It's pretty easy to see why that sort of thing would be troubling to a progressively inclined individual.