Angels are born in heaven, not earth.
Man will always have avarice, anger, and jealousy within him.
There will never be a time where everyone just gets along merrily without conflict of some nature whether it be micro (hey, who took my apple?) or macro (hey, a bunch of bandits are coming over the hill to take our land).
Lust, gluttony, greed, and any other vice you can think of will always be present in some form, no matter how homogeneous or upstanding the society is, and always lead to a dispute of some kind.
The universe is built on order. And if a society does not have order (laws) whether written down, or known colloquially, and more specifically if not enforced, the society will crumble in an all out free for all where the most ruthless reign.
A constitution or set edicts is necessary and always will be
People won't be good just for goodness sake