The whole world being a body and the Rebbe being the brain just sounds like unambiguous elokism to me. Your putting the Rebbe on a level above where we traditionally put the (not yet here) Moshiach.
I mostly agree with Syag. The only thing I would say is in regards to the comparison about the woman who thinks she should be able to wear loose pants:
When a religious left-wing, bareheaded, pants-wearing, gemarra-learning woman comes over and asks “why do you think it’s not tznius to wear pants?” 99 times out of 100, she isn’t at all interested in your halachic answer. She’s already made it very clear that she hates and denies the halachah, and most likely it is just a warm up to an attack. Throughout the internet, most of the sites dedicated to criticizing or “questioning” Chabad, are not written by learned, inquisitive people. They really are just attackers. It’s possible that it’s conditioned Lubavitchers to getting so defensive so quickly.