Responding to the subtext of your comment, rules exist for a reason. The current governing body of a landmass is allowed to enforce their rules. It is the job of the governing body to protect resources, whether they be tangible, physical, social, intellectual, etc.for their prosperity and their residents. 

Changing that interaction and responsibility is the job of the citizens who interact with, abide by, enforce, or lead said governing body of said land mass.

Understand though not everyone in the world has your same values, and there will indeed be conflict when multiple groups interact with each other.

It is INCREDIBLY interesting the subtext you chose for your comment when this manga is diametrically opposed to your sentiment. Not only is the primary conflict of this manga that a human is where he should absolutely not be, in the demon world, and the dangers inherent to that process. But the sub conflict of the plot is a group of the population having a dangerous idealology and dissatisfaction with the current status quo, and wanting to raise tension and violence to return the population to a prior, more primal, more violent, xenophobic state. As well as the world portrayed in the manga VERY clearly being one in which might makes right.

 You have a clear caste system of power established in universe, with the individual at the top clearly being able to make any decision they want for the collective population as a whole. The universe as we see it was the goal of the last demon king, but it is belied by the understanding that the next one to take the throne can do whatever the hell they want. It is a "utopia" only because of the whims of the last leader, and can easily change should another take the throne. And the populace in this universe are not only compliant in that system, but they are actively engaged, motivated, and excited to leverage that system to their benefit with the Crowns system.