Its because among honest people that works perfectly fine.

As a cultural example, look at haggling. In America it's viewed as kind quirky at best and downright rude at worst. Price tags exist for a reason, and they present absolute offer. That faith in what you might call "the sanctity of public notice" only exists in a high trust society. The notion of win-win. Of choosing option A in the prisoners dilemma.

If in your core of core you believe in those ideals, it's much harder to set them aside than it is for somebody who doesn't believe in them at all.

Its the same idea as the whole "politeness without capacity for violence is just begging"