"I don't know why the notion of different brain chemistry is so threatening to some groups, but it is what it is."

Maybe because such notions have historically been and still are used to justify biases that underly sexist behavior such as that studied here: http://news.wustl.edu/news/Pages/6414.aspx

This is just a modern day spin on phrenology (https://en.wikipedia.org/wiki/Phrenology). Remember how scientists once looked for a link between face symmetry and criminality? Good times.