Cruel and unusual/ Reasonable creature

How do we decide what is cruel and unusual?

We are so subjective in this matter. I think that people grow up in different environments that make defining this nearly impossible. If we use the example we talked about in class of a person who has grown up in a prison environment vs. someone who is born into a more passive and gentle environment their ideas of what is acceptable as punishment is going to be different. I wonder if there is even a way to accommodate the two perceptions. Of course what makes it harder is that their are so many different opinions on what is acceptable. I think this just goes back to the law and the ambiguity that can be found in this subject.

Something I also question is the idea of intent of the crime and liability. Dayan brings up for a bit the "mental awareness"  of the person who has committed a crime. By going and doing this unlawful thing the person has killed off the "reasonable creature." This idea reminds me of the current trend of criminals and using mental instability as an excuse for their crimes. So we reach a sort of paradox where if the person is full aware of the intent to do the crime have they lost their "reasonable creature" and in turn become mentally unstable or experience a loss of reason? Or was it a fully rational choice?
There are many things we have started to take into account for criminals; such as their background history of child rearing they experienced, how they were in school, documented cases of mental problems, etc. But when do we draw the line that they made a ration choice to succumb to these problems? Their are people who do grow up in awful environments but choose to rise above it. So there must people be people who choose to let it affect them. Now I know that we do have to note that those who grow up in this situations are usually in a lower income/minority/etc. background and there are forces that do hold them back in a way that doesn't hold someone back of a better situation. But people from all sorts of  backgrounds commit crimes. Where do we loose the rational thinking? When do they no longer become a "reasonable creature"? Or are they in their own way being reasonable about their choice?

This was something that stood out to me a lot in the reading, so I only really wrote about this topic and some of the questions that come forth, I haven't thought much into my own answers yet for them.