This is a great question. I wish there was a bit more in terms of context (the first sentence starts in the middle), but from the words that you give, a few points can be made.
First, the author is stating that there is confusion among girls of how to act. Hence, girls are drawn to more "traditional" displays of masculinity on account of uncertainty of their own gender identity.
Second, the author, then, talk about his or her son and how there might be confusion as well.
Finally, here is the crux of the matter. The author states that there is a need to critique and reform culture, because culture blurs what it means to be a boy or girl. The cultural imperative is what the culture imposes on people are common sense and accepted. This is the assumption that the authors wants to call into question