Interesting questions, Hannah, especially the last part. I used to think that works of literature should be assessed (I don't like the word 'criticised', it has too many negative connotations) purely on its own merits. While I still shy away from trying to use a text to surmise something about the author's life or state of mind, I now think no work should be taken in isolation. Everything, to my way of thinking, is part of a whole, part of the Zeitgeist, if you like, and the more a reader understands about the period in which the work was written, the more likely it is that he/she will come close to understanding the writer's intentions.
In fact, I think it is quite dangerous to read any 'old' work with modern sensibilities alone - and by 'old', I'd certainly include anything more than twenty, or even ten, years old. In case you are thinking I'm being too stringent in my timing, let me suggest to you that you think for example about the changes in attitudes to money as recently as 2008 following the financial crises that began in the autumn of that year. As for social attitudes, when I was a child, (granted a long time ago,

) the word 'divorce' was whispered in hushed and shamed tones. It seems to me that unless you have some understanding of the mores of the time the book/play/treatise was written, you will not fully understand the work.