No, that's the thing, you all have to expect them to be reasonable. They know this, and its social pressure to actually be reasonable. That's how the whole thing works. And then of course, you forgive someone who for whatever emotional reason cannot be reasonable for some brief time. Because, all human.
And this expectation actually have to be emotional. Because, paradoxically, human behavior is guided by emotions, not reason.
No, but it sets a standard of interaction and expectations for how conflict should be dealt with.
"Expecting" everyone within a group to be reasonable is another way of saying: if you are consistently unreasonable, you won't be considered part of the group.
The text is worse than that, it says "expect everyone to be reasonable", not "everyone within a group". In a group of have shared interests and shared needs, but leadership is different, it responds to different social pressure. If leadership is dysfunctional you have a problem, and no amount of kumbaya is going to help.