relations really is quite complex in TK and anything that does happen is
based on your relationship with that faction or factions. There is some
exceptions to this though such as random stalkers or factions members
being red at you while others are green or yellow. That aspect is not
based on your reputation, but the NPCs reputation. The lower the NPCs
reputation, the more chance there is of him turning on you because hes
considered somewhat of a rouge.
Lets say you helped both Duty and Freedom quite a lot, to the point of which
both factions considered you _almost_ their friend. As a result your
reputation with both factions is quite high, so if both sides started
shooting at eachother with you in the immediate vicinity, they both
would expect you to help them out. If you don't both
sides will end up hating you. They trusted you, and you betrayed them as far as
they see it. Their attitude is now "the enemy of my enemy".
Hope that helps explain the relations in TK :)