Final answer:
Other centaurs besides Firenze in 'Harry Potter and the Sorcerer's Stone' refuse to help Harry because of their strict belief in non-interference and the pre-determined nature of destiny.
Step-by-step explanation:
In Harry Potter and the Sorcerer's Stone, Chapter 15, the other centaurs besides Firenze are against helping Harry Potter because they believe in adhering to a strict policy of non-interference in the affairs of humans. Centaurs, in their culture and view of the cosmos, place great importance on allowing the future to unfold without their intervention, as they believe destinies are pre-determined by the stars. Firenze breaks with this tradition by assisting Harry, which angers the other centaurs who feel it is not their place to interfere with what they see as the natural course of events and the fulfillment of prophecies.