Originally posted by Jyn
By my logic, any schizophrenic who doesn't reliably take medication and has a history of killing, mutilating, and eating people should be summarily executed, yes. In the interest of preventing future acts committed by the same person. If a particular schizophrenic has never done so before, then there is no prior evidence that he/she will do so in the future, is there?
(some emphasis mine)

So, you're proposing that we use the prior history of the insane to predict their potential danger to society in the future.

Originally posted by Jyn
people are unpredictable, no matter what kind of pattern of behavior they show for any length of time.
...
As I said, human behavior is unpredictable. You cannot count on a person who lived a pattern of complete non-violence for 30 years of their life to not commit murder in the 31st year.
Your two statements seem to be entirely contradictory.

Originally posted by Jyn
they are not, nor should they be, excused for their past.
So you think that people should be held criminally liable even if they are truly insane. The insane have a diminished capacity for rational thought. If you think that's not an excuse, then for consistency, you should also approve of adult criminal penalties being applied to children of any age for their actions. If a toddler burns a house down while playing with matches, should they be charged with arson and be locked up? They certainly shouldn't ever be excused for their past, right?

Originally posted by Jyn
it is how our society and its laws work (at least in the US).
In western society, including the US, criminal liability is related to sanity.

Originally posted by Jyn
I'm not claiming to know more about psychiatry than psychiatrists.
Yes you are. See below.
Originally posted by Jyn
A few years go by, he'll miraculously improve, and they'll let him out.
You clearly think that the medical professionals in question will release a subject who hasn't legitimately improved in their condition. You also clearly think that they are wrong and you are right regarding the possibility of a subject with a mental condition recovering and living a peaceful, productive life afterwards.