They usually also peacefully agree on punishment for other people if those break the law. Even if the latter disagree about whether they should be punished. And if they try to resist the punishment, it usually results in more punishment.

The larger a group of people, the less likely it is that they would all agree on something. Ten people can agree on something; ten millions agreeing on something is extremely improbable.

Trevor's comment is irrelevant to the thought experiment (thus the downvotes), but it is technically correct.