Theorists:

1) Laura Mulvey:
http://www.aber.ac.uk/media/Documents/gaze/gaze09.html

The Male Gaze has it assumed that the male audience will grasp an appealing sight from women on the big screen. The gaze applies to Sin City unsurprisingly of its genre. We get an example of this when Nancy is poll-dancing.

2) Vladimir Proop:
http://64.233.183.104/search?q=cache:DOq964fLQTMJ:www.cfe.lu.se/CFEWP/CFEPaper29.pdf+propp+theory+of+whore+madonna+&hl=en

The idea that females take on one of four roles as either the Madonna, the Whore, the Wife, or the Femme Fatale. In Sin City, there are examples of all of these classes.

3) Sigmund Frued:
http://www.psybox.com/web_dictionary/Penisenvy.htm

Penis envy theory which seems unlikely, yet there it is. It states that daughters at a young age discover they lack male genitals, subsequently blame their mother for this, and turn to their father for love. In what way, I’m glad it isn’t stated. There is a possible hint of this in one scene in Sin City with one of the characters.