A character's rationality isn't something which can be helped,
I'm pretty sure education can improve somebody's rationality.
but to what extent does that allow a person to escape critcism?
We should be criticising the behaviour - criticising the person achieves nothing.
Is a persons bad spelling always down to their dyslexic tendancies?
No, it's down to poor education.
Is a depressed persons misery always out of their control?
No, but the ability to control it can be improved with cognitive therapy & by learning how to deal with negative emotions or bad situations - emotional control is like any other skill & can be learned.
Should murderers be immune to criticism because they are clearly not right in the head?
The act of murder should not be immune from criticism & they should still be locked up (for the safety of others).
But labelling a person (who either eats too much, rapes people or murders) - as simply "Bad or evil" solves nothing, it does not advance our understanding of the behaviour.
For example, if you label paedophiles as "evil" & attribute the actions as factors inherent to the individual - how exactly we will ever stop these actions from occurring?.
Saying "peado's are evil lock them up" & ending the discussion, does nothing for the next wave of children who will become victims - punishment & blame are too late in these situations, the offence has already happened.
More-so when the evidence suggests that most negative behaviour is stemmed from early childhood experiences
I'm not expecting you to answer these, my point merely being that a mental issue does not necessarily always mean that those people are free of their own responsibility.
Define responsibility, when we are biological organisms who are slaves to our experiences, biology & environment?.
People need to let go of these mostly religious based notions of "personal responsibility" & accept reality for what it is - I'm not suggesting that people who believe in it are religious - but those are the roots of it.