Wait--I eat chicken cheesesteaks all the time (well, not *all* the time, but fairly often), and I don't think they're sacrilege. But then, I'm not a Philly native--just lived there forever and a day. :-)
Neither Pat's nor Geno's were my favorite. To me, those represent a Platonic form, whereas the cheesesteaks I encountered were from reality. I especially liked the cheesesteaks from corner stores in my neighborhood--particularly Kimey's just south of the corner of 33rd and Spring Garden.
I used to live in Philadelphia (33rd and Spring Garden) and sometimes I really really really miss getting a cheesesteak. Whenever I go somewhere on the west coast has a "good" cheesesteak, there is disappointment; it might be "good," but it is no "cheesesteak."